diff --git a/app/api/projects/[projectId]/members/[userId]/route.ts b/app/api/projects/[projectId]/members/[userId]/route.ts
new file mode 100644
index 0000000..8977c5c
--- /dev/null
+++ b/app/api/projects/[projectId]/members/[userId]/route.ts
@@ -0,0 +1,30 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getCurrentUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService } from '@/lib/api/services';
+import { UnauthorizedError } from '@/lib/errors';
+import { handleApiError } from '@/lib/api/handleError';
+
+export const runtime = 'nodejs';
+
+export async function DELETE(
+  _request: NextRequest,
+  {
+    params,
+  }: {
+    params: Promise<{ projectId: string; userId: string }>;
+  }
+) {
+  const user = await getCurrentUser();
+  if (!user) {
+    return handleApiError(new UnauthorizedError());
+  }
+  const { projectId, userId } = await params;
+
+  const service = createProjectService();
+  try {
+    service.removeMember(user.id, Number(projectId), Number(userId));
+    return NextResponse.json({ ok: true });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
diff --git a/app/api/projects/[projectId]/members/route.ts b/app/api/projects/[projectId]/members/route.ts
new file mode 100644
index 0000000..642306f
--- /dev/null
+++ b/app/api/projects/[projectId]/members/route.ts
@@ -0,0 +1,69 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getCurrentUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService, createUserRepository } from '@/lib/api/services';
+import { UnauthorizedError, NotFoundError } from '@/lib/errors';
+import { handleApiError, jsonError } from '@/lib/api/handleError';
+import type { ProjectMemberRole } from '@/lib/types';
+
+export const runtime = 'nodejs';
+
+export async function GET(
+  _request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) {
+    return handleApiError(new UnauthorizedError());
+  }
+  const { projectId } = await params;
+
+  const service = createProjectService();
+  try {
+    const members = service.getMembers(user.id, Number(projectId));
+    return NextResponse.json({ members });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
+
+export async function POST(
+  request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) {
+    return handleApiError(new UnauthorizedError());
+  }
+  const { projectId } = await params;
+
+  let body: Record<string, unknown>;
+  try {
+    body = (await request.json()) as Record<string, unknown>;
+  } catch {
+    return jsonError(400, 'リクエスト本文が不正です');
+  }
+
+  const email = String(body.email ?? '');
+  const role = (
+    typeof body.role === 'string' ? body.role : 'member'
+  ) as ProjectMemberRole;
+
+  // メールアドレスからユーザーを解決する
+  const targetUser = createUserRepository().findByEmail(email);
+  if (!targetUser) {
+    return handleApiError(new NotFoundError('User', email));
+  }
+
+  const service = createProjectService();
+  try {
+    const member = service.addMember(
+      user.id,
+      Number(projectId),
+      targetUser.id,
+      role
+    );
+    return NextResponse.json({ member }, { status: 201 });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
diff --git a/app/api/projects/[projectId]/route.ts b/app/api/projects/[projectId]/route.ts
new file mode 100644
index 0000000..9c1028c
--- /dev/null
+++ b/app/api/projects/[projectId]/route.ts
@@ -0,0 +1,79 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getCurrentUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService } from '@/lib/api/services';
+import { UnauthorizedError } from '@/lib/errors';
+import { handleApiError, jsonError } from '@/lib/api/handleError';
+
+export const runtime = 'nodejs';
+
+export async function GET(
+  _request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) {
+    return handleApiError(new UnauthorizedError());
+  }
+  const { projectId } = await params;
+
+  const service = createProjectService();
+  try {
+    const dashboard = service.getDashboard(user.id, Number(projectId));
+    return NextResponse.json(dashboard);
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
+
+export async function PATCH(
+  request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) {
+    return handleApiError(new UnauthorizedError());
+  }
+  const { projectId } = await params;
+
+  let body: Record<string, unknown>;
+  try {
+    body = (await request.json()) as Record<string, unknown>;
+  } catch {
+    return jsonError(400, 'リクエスト本文が不正です');
+  }
+
+  const service = createProjectService();
+  try {
+    const project = service.updateProject(user.id, Number(projectId), {
+      name: typeof body.name === 'string' ? body.name : undefined,
+      description:
+        typeof body.description === 'string' ? body.description : undefined,
+      status:
+        typeof body.status === 'string'
+          ? (body.status as 'active' | 'on_hold' | 'completed' | 'archived')
+          : undefined,
+    });
+    return NextResponse.json({ project });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
+
+export async function DELETE(
+  _request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) {
+    return handleApiError(new UnauthorizedError());
+  }
+  const { projectId } = await params;
+
+  const service = createProjectService();
+  try {
+    service.deleteProject(user.id, Number(projectId));
+    return NextResponse.json({ ok: true });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
diff --git a/app/api/projects/route.ts b/app/api/projects/route.ts
new file mode 100644
index 0000000..6e7be29
--- /dev/null
+++ b/app/api/projects/route.ts
@@ -0,0 +1,43 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getCurrentUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService } from '@/lib/api/services';
+import { UnauthorizedError } from '@/lib/errors';
+import { handleApiError, jsonError } from '@/lib/api/handleError';
+
+export const runtime = 'nodejs';
+
+export async function GET() {
+  const user = await getCurrentUser();
+  if (!user) {
+    return handleApiError(new UnauthorizedError());
+  }
+  const service = createProjectService();
+  const projects = service.getMyProjects(user.id);
+  return NextResponse.json({ projects });
+}
+
+export async function POST(request: NextRequest) {
+  const user = await getCurrentUser();
+  if (!user) {
+    return handleApiError(new UnauthorizedError());
+  }
+
+  let body: Record<string, unknown>;
+  try {
+    body = (await request.json()) as Record<string, unknown>;
+  } catch {
+    return jsonError(400, 'リクエスト本文が不正です');
+  }
+
+  const service = createProjectService();
+  try {
+    const project = service.createProject(user.id, {
+      name: String(body.name ?? ''),
+      description:
+        typeof body.description === 'string' ? body.description : undefined,
+    });
+    return NextResponse.json({ project }, { status: 201 });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
diff --git a/app/dashboard/page.tsx b/app/dashboard/page.tsx
index 657490d..253da87 100644
--- a/app/dashboard/page.tsx
+++ b/app/dashboard/page.tsx
@@ -1,5 +1,9 @@
 import { redirect } from 'next/navigation';
-import { getCurrentUser } from '@/lib/auth/getCurrentUser';
+import { getCurrentUser, toPublicUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService } from '@/lib/api/services';
+import { Header } from '@/components/layout/Header';
+import { ProjectCard } from '@/components/project/ProjectCard';
+import { CreateProjectForm } from '@/components/project/CreateProjectForm';
 
 export const dynamic = 'force-dynamic';
 
@@ -9,19 +13,32 @@ export default async function DashboardPage() {
     redirect('/login');
   }
 
+  const service = createProjectService();
+  const projects = service.getMyProjects(user.id);
+
   return (
-    <main className="min-h-screen bg-gray-50 p-8">
-      <div className="mx-auto max-w-3xl">
-        <div className="flex items-center justify-between">
-          <h1 className="text-2xl font-bold">ダッシュボード</h1>
-          <a href="/profile" className="text-sm text-blue-600 hover:underline">
-            {user.name} さん
-          </a>
-        </div>
-        <p className="mt-4 text-gray-600">
-          プロジェクト機能は後続マイルストーンで実装されます。
-        </p>
-      </div>
-    </main>
+    <div className="min-h-screen bg-gray-50">
+      <Header user={toPublicUser(user)} />
+      <main className="mx-auto max-w-4xl space-y-6 p-6">
+        <h1 className="text-2xl font-bold">ダッシュボード</h1>
+        <CreateProjectForm />
+        <section>
+          <h2 className="mb-3 text-sm font-semibold text-gray-700">
+            参加プロジェクト
+          </h2>
+          {projects.length === 0 ? (
+            <p className="text-sm text-gray-400">
+              参加しているプロジェクトはありません。
+            </p>
+          ) : (
+            <div className="grid gap-3 sm:grid-cols-2">
+              {projects.map((project) => (
+                <ProjectCard key={project.id} project={project} />
+              ))}
+            </div>
+          )}
+        </section>
+      </main>
+    </div>
   );
 }
diff --git a/app/projects/[projectId]/members/page.tsx b/app/projects/[projectId]/members/page.tsx
new file mode 100644
index 0000000..6dbb4d1
--- /dev/null
+++ b/app/projects/[projectId]/members/page.tsx
@@ -0,0 +1,86 @@
+import { redirect } from 'next/navigation';
+import { getCurrentUser, toPublicUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService } from '@/lib/api/services';
+import { Header } from '@/components/layout/Header';
+import { ProjectNav } from '@/components/layout/ProjectNav';
+import { AddMemberForm } from '@/components/project/AddMemberForm';
+import { RemoveMemberButton } from '@/components/project/RemoveMemberButton';
+import { ForbiddenError, NotFoundError } from '@/lib/errors';
+
+export const dynamic = 'force-dynamic';
+
+const ROLE_LABEL = { admin: '管理者', member: 'メンバー', guest: 'ゲスト' };
+
+export default async function ProjectMembersPage({
+  params,
+}: {
+  params: Promise<{ projectId: string }>;
+}) {
+  const user = await getCurrentUser();
+  if (!user) {
+    redirect('/login');
+  }
+  const { projectId } = await params;
+
+  const service = createProjectService();
+  let project: Awaited<ReturnType<typeof service.getProject>>;
+  let members: Awaited<ReturnType<typeof service.getMembers>>;
+  let canManage: boolean;
+  try {
+    project = service.getProject(user.id, Number(projectId));
+    members = service.getMembers(user.id, Number(projectId));
+    canManage = service.getMemberRole(user.id, Number(projectId)) === 'admin';
+  } catch (error) {
+    if (error instanceof ForbiddenError || error instanceof NotFoundError) {
+      redirect('/dashboard');
+    }
+    throw error;
+  }
+
+  return (
+    <div className="min-h-screen bg-gray-50">
+      <Header user={toPublicUser(user)} />
+      <ProjectNav projectId={project.id} active="members" />
+      <main className="mx-auto max-w-3xl space-y-6 p-6">
+        <h1 className="text-2xl font-bold">メンバー管理</h1>
+
+        {canManage && <AddMemberForm projectId={project.id} />}
+
+        <section className="rounded-lg border bg-white shadow-sm">
+          <ul className="divide-y">
+            {members.map((member) => (
+              <li
+                key={member.id}
+                className="flex items-center justify-between p-4"
+              >
+                <div>
+                  <p className="font-medium text-gray-800">
+                    {member.user.name}
+                    {member.userId === user.id && (
+                      <span className="ml-2 text-xs text-gray-400">
+                        (あなた)
+                      </span>
+                    )}
+                  </p>
+                  <p className="text-sm text-gray-500">{member.user.email}</p>
+                </div>
+                <div className="flex items-center gap-3">
+                  <span className="text-sm text-gray-600">
+                    {ROLE_LABEL[member.role] ?? member.role}
+                  </span>
+                  {canManage && member.userId !== user.id && (
+                    <RemoveMemberButton
+                      projectId={project.id}
+                      userId={member.userId}
+                      label="削除"
+                    />
+                  )}
+                </div>
+              </li>
+            ))}
+          </ul>
+        </section>
+      </main>
+    </div>
+  );
+}
diff --git a/app/projects/[projectId]/page.tsx b/app/projects/[projectId]/page.tsx
new file mode 100644
index 0000000..9a0d3d2
--- /dev/null
+++ b/app/projects/[projectId]/page.tsx
@@ -0,0 +1,79 @@
+import { redirect } from 'next/navigation';
+import { getCurrentUser, toPublicUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService } from '@/lib/api/services';
+import { Header } from '@/components/layout/Header';
+import { ProjectNav } from '@/components/layout/ProjectNav';
+import { DashboardWidget } from '@/components/project/DashboardWidget';
+import { ForbiddenError, NotFoundError } from '@/lib/errors';
+
+export const dynamic = 'force-dynamic';
+
+const STATUS_LABELS: Record<string, string> = {
+  active: 'Active',
+  on_hold: 'On Hold',
+  completed: 'Completed',
+  archived: 'Archived',
+};
+
+export default async function ProjectOverviewPage({
+  params,
+}: {
+  params: Promise<{ projectId: string }>;
+}) {
+  const user = await getCurrentUser();
+  if (!user) {
+    redirect('/login');
+  }
+  const { projectId } = await params;
+
+  const service = createProjectService();
+  let dashboard;
+  try {
+    dashboard = service.getDashboard(user.id, Number(projectId));
+  } catch (error) {
+    if (error instanceof ForbiddenError || error instanceof NotFoundError) {
+      redirect('/dashboard');
+    }
+    throw error;
+  }
+
+  const { project, members } = dashboard;
+
+  return (
+    <div className="min-h-screen bg-gray-50">
+      <Header user={toPublicUser(user)} />
+      <ProjectNav projectId={project.id} active="overview" />
+      <main className="mx-auto max-w-4xl space-y-6 p-6">
+        <div className="flex items-center justify-between">
+          <h1 className="text-2xl font-bold">{project.name}</h1>
+          <span className="rounded bg-gray-100 px-2 py-0.5 text-xs">
+            {STATUS_LABELS[project.status] ?? project.status}
+          </span>
+        </div>
+        {project.description && (
+          <p className="text-gray-600">{project.description}</p>
+        )}
+        <p className="text-sm text-gray-500">メンバー数: {members.length}</p>
+
+        <div className="grid gap-4 sm:grid-cols-2">
+          <DashboardWidget
+            title="進行中ToDo"
+            empty="ToDo機能は後続マイルストーンで実装されます"
+          />
+          <DashboardWidget
+            title="最新チャット"
+            empty="チャット機能は後続マイルストーンで実装されます"
+          />
+          <DashboardWidget
+            title="最新掲示板"
+            empty="掲示板機能は後続マイルストーンで実装されます"
+          />
+          <DashboardWidget
+            title="最近のアクティビティ"
+            empty="アクティビティログは後続マイルストーンで実装されます"
+          />
+        </div>
+      </main>
+    </div>
+  );
+}
diff --git a/app/projects/[projectId]/settings/page.tsx b/app/projects/[projectId]/settings/page.tsx
new file mode 100644
index 0000000..582d901
--- /dev/null
+++ b/app/projects/[projectId]/settings/page.tsx
@@ -0,0 +1,57 @@
+import { redirect } from 'next/navigation';
+import { getCurrentUser, toPublicUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService } from '@/lib/api/services';
+import { Header } from '@/components/layout/Header';
+import { ProjectNav } from '@/components/layout/ProjectNav';
+import { ProjectSettingsForm } from '@/components/project/ProjectSettingsForm';
+import { DeleteProjectButton } from '@/components/project/DeleteProjectButton';
+import { ForbiddenError, NotFoundError } from '@/lib/errors';
+
+export const dynamic = 'force-dynamic';
+
+export default async function ProjectSettingsPage({
+  params,
+}: {
+  params: Promise<{ projectId: string }>;
+}) {
+  const user = await getCurrentUser();
+  if (!user) {
+    redirect('/login');
+  }
+  const { projectId } = await params;
+
+  const service = createProjectService();
+  let project;
+  let canManage;
+  try {
+    project = service.getProject(user.id, Number(projectId));
+    canManage = service.getMemberRole(user.id, Number(projectId)) === 'admin';
+  } catch (error) {
+    if (error instanceof ForbiddenError || error instanceof NotFoundError) {
+      redirect('/dashboard');
+    }
+    throw error;
+  }
+
+  return (
+    <div className="min-h-screen bg-gray-50">
+      <Header user={toPublicUser(user)} />
+      <ProjectNav projectId={project.id} active="settings" />
+      <main className="mx-auto max-w-2xl space-y-6 p-6">
+        <h1 className="text-2xl font-bold">プロジェクト設定</h1>
+        <div className="rounded-lg border bg-white p-6 shadow-sm">
+          <ProjectSettingsForm project={project} canManage={canManage} />
+        </div>
+        {canManage && (
+          <div className="rounded-lg border border-red-200 bg-white p-6 shadow-sm">
+            <h2 className="text-sm font-semibold text-red-700">危険操作</h2>
+            <p className="mt-1 text-sm text-gray-600">
+              プロジェクトを削除すると、関連データも削除されます。
+            </p>
+            <DeleteProjectButton projectId={project.id} />
+          </div>
+        )}
+      </main>
+    </div>
+  );
+}
diff --git a/components/layout/Header.tsx b/components/layout/Header.tsx
new file mode 100644
index 0000000..c99bf34
--- /dev/null
+++ b/components/layout/Header.tsx
@@ -0,0 +1,37 @@
+'use client';
+
+import { useRouter } from 'next/navigation';
+import type { PublicUser } from '@/lib/auth/getCurrentUser';
+
+export function Header({ user }: { user: PublicUser }) {
+  const router = useRouter();
+
+  async function handleLogout() {
+    await fetch('/api/auth/logout', { method: 'POST' });
+    router.push('/login');
+    router.refresh();
+  }
+
+  return (
+    <header className="flex items-center justify-between border-b bg-white px-6 py-3">
+      <a href="/dashboard" className="font-bold text-gray-800">
+        シンプルグループウェア
+      </a>
+      <nav className="flex items-center gap-4 text-sm">
+        <a href="/dashboard" className="text-gray-600 hover:underline">
+          ダッシュボード
+        </a>
+        <a href="/profile" className="text-gray-600 hover:underline">
+          {user.name} さん
+        </a>
+        <button
+          type="button"
+          onClick={handleLogout}
+          className="text-blue-600 hover:underline"
+        >
+          ログアウト
+        </button>
+      </nav>
+    </header>
+  );
+}
diff --git a/components/layout/ProjectNav.tsx b/components/layout/ProjectNav.tsx
new file mode 100644
index 0000000..9ceeaaa
--- /dev/null
+++ b/components/layout/ProjectNav.tsx
@@ -0,0 +1,45 @@
+const NAV_ITEMS = [
+  { href: '', label: '概要' },
+  { href: '/members', label: 'メンバー' },
+  { href: '/settings', label: '設定' },
+] as const;
+
+/**
+ * プロジェクト内サブナビゲーション。
+ * href は `/projects/{projectId}` を起点とする相対パス。
+ */
+export function ProjectNav({
+  projectId,
+  active,
+}: {
+  projectId: number;
+  active: 'overview' | 'members' | 'settings';
+}) {
+  const activeMap: Record<string, boolean> = {
+    overview: active === 'overview',
+    members: active === 'members',
+    settings: active === 'settings',
+  };
+
+  return (
+    <nav className="flex gap-4 border-b bg-white px-6 py-2 text-sm">
+      {NAV_ITEMS.map((item) => {
+        const key = item.href === '' ? 'overview' : item.href.slice(1);
+        const href = `/projects/${projectId}${item.href}`;
+        return (
+          <a
+            key={item.href}
+            href={href}
+            className={
+              activeMap[key]
+                ? 'font-medium text-blue-600'
+                : 'text-gray-600 hover:underline'
+            }
+          >
+            {item.label}
+          </a>
+        );
+      })}
+    </nav>
+  );
+}
diff --git a/components/layout/Sidebar.tsx b/components/layout/Sidebar.tsx
new file mode 100644
index 0000000..ec14289
--- /dev/null
+++ b/components/layout/Sidebar.tsx
@@ -0,0 +1,9 @@
+/**
+ * プロジェクトページ共通のサイドバー。
+ * プロジェクト内ナビゲーションは ProjectNav に委譲する。
+ */
+export function Sidebar({ children }: { children: React.ReactNode }) {
+  return (
+    <aside className="w-48 shrink-0 border-r bg-gray-50 p-4">{children}</aside>
+  );
+}
diff --git a/components/project/AddMemberForm.tsx b/components/project/AddMemberForm.tsx
new file mode 100644
index 0000000..a1d1d0e
--- /dev/null
+++ b/components/project/AddMemberForm.tsx
@@ -0,0 +1,84 @@
+'use client';
+
+import { useState, type FormEvent } from 'react';
+import { useRouter } from 'next/navigation';
+
+export function AddMemberForm({ projectId }: { projectId: number }) {
+  const router = useRouter();
+  const [email, setEmail] = useState('');
+  const [role, setRole] = useState('member');
+  const [error, setError] = useState<string | null>(null);
+  const [loading, setLoading] = useState(false);
+
+  async function onSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setLoading(true);
+    setError(null);
+
+    const res = await fetch(`/api/projects/${projectId}/members`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ email, role }),
+    });
+
+    if (res.ok) {
+      setEmail('');
+      router.refresh();
+      return;
+    }
+
+    const body = (await res.json().catch(() => null)) as {
+      error?: { message?: string };
+    } | null;
+    setError(body?.error?.message ?? 'メンバー追加に失敗しました');
+    setLoading(false);
+  }
+
+  return (
+    <form
+      onSubmit={onSubmit}
+      className="flex flex-col gap-2 rounded border bg-white p-4 sm:flex-row sm:items-end"
+    >
+      <div className="flex-1">
+        <label htmlFor="member-email" className="block text-sm font-medium">
+          追加するユーザーのメールアドレス
+        </label>
+        <input
+          id="member-email"
+          type="email"
+          value={email}
+          onChange={(e) => setEmail(e.target.value)}
+          className="mt-1 w-full rounded border px-3 py-2"
+          required
+        />
+      </div>
+      <div>
+        <label htmlFor="member-role" className="block text-sm font-medium">
+          ロール
+        </label>
+        <select
+          id="member-role"
+          value={role}
+          onChange={(e) => setRole(e.target.value)}
+          className="mt-1 rounded border px-3 py-2"
+        >
+          <option value="member">member</option>
+          <option value="admin">admin</option>
+          <option value="guest">guest</option>
+        </select>
+      </div>
+      <button
+        type="submit"
+        disabled={loading}
+        className="rounded bg-blue-600 px-4 py-2 font-medium text-white hover:bg-blue-700 disabled:opacity-50"
+      >
+        {loading ? '追加中...' : 'メンバー追加'}
+      </button>
+      {error && (
+        <p className="text-sm text-red-600" role="alert">
+          {error}
+        </p>
+      )}
+    </form>
+  );
+}
diff --git a/components/project/CreateProjectForm.tsx b/components/project/CreateProjectForm.tsx
new file mode 100644
index 0000000..4faf363
--- /dev/null
+++ b/components/project/CreateProjectForm.tsx
@@ -0,0 +1,85 @@
+'use client';
+
+import { useState, type FormEvent } from 'react';
+import { useRouter } from 'next/navigation';
+
+export function CreateProjectForm() {
+  const router = useRouter();
+  const [name, setName] = useState('');
+  const [description, setDescription] = useState('');
+  const [error, setError] = useState<string | null>(null);
+  const [loading, setLoading] = useState(false);
+
+  async function onSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setLoading(true);
+    setError(null);
+
+    const res = await fetch('/api/projects', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ name, description: description || undefined }),
+    });
+
+    if (res.ok) {
+      const data = (await res.json()) as { project: { id: number } };
+      router.push(`/projects/${data.project.id}`);
+      return;
+    }
+
+    const body = (await res.json().catch(() => null)) as {
+      error?: { message?: string };
+    } | null;
+    setError(body?.error?.message ?? 'プロジェクトの作成に失敗しました');
+    setLoading(false);
+  }
+
+  return (
+    <form
+      onSubmit={onSubmit}
+      className="flex flex-col gap-2 rounded-lg border bg-white p-4 shadow-sm sm:flex-row sm:items-end"
+    >
+      <div className="flex-1">
+        <label htmlFor="project-name" className="block text-sm font-medium">
+          プロジェクト名
+        </label>
+        <input
+          id="project-name"
+          type="text"
+          value={name}
+          onChange={(e) => setName(e.target.value)}
+          className="mt-1 w-full rounded border px-3 py-2"
+          required
+          maxLength={200}
+        />
+      </div>
+      <div className="flex-1">
+        <label
+          htmlFor="project-description"
+          className="block text-sm font-medium"
+        >
+          説明（任意）
+        </label>
+        <input
+          id="project-description"
+          type="text"
+          value={description}
+          onChange={(e) => setDescription(e.target.value)}
+          className="mt-1 w-full rounded border px-3 py-2"
+        />
+      </div>
+      <button
+        type="submit"
+        disabled={loading}
+        className="rounded bg-blue-600 px-4 py-2 font-medium text-white hover:bg-blue-700 disabled:opacity-50"
+      >
+        {loading ? '作成中...' : '新規プロジェクト'}
+      </button>
+      {error && (
+        <p className="text-sm text-red-600 sm:full" role="alert">
+          {error}
+        </p>
+      )}
+    </form>
+  );
+}
diff --git a/components/project/DashboardWidget.tsx b/components/project/DashboardWidget.tsx
new file mode 100644
index 0000000..44909b5
--- /dev/null
+++ b/components/project/DashboardWidget.tsx
@@ -0,0 +1,24 @@
+/**
+ * ダッシュボードの各項目を表示するウィジェットコンテナ。
+ * M4では骨組みのみ。全項目の集計は M13 で完成させる。
+ */
+export function DashboardWidget({
+  title,
+  children,
+  empty,
+}: {
+  title: string;
+  children?: React.ReactNode;
+  empty?: string;
+}) {
+  return (
+    <section className="rounded-lg border bg-white p-4 shadow-sm">
+      <h2 className="mb-3 text-sm font-semibold text-gray-700">{title}</h2>
+      {children ? (
+        <div className="space-y-2">{children}</div>
+      ) : (
+        <p className="text-sm text-gray-400">{empty ?? 'データがありません'}</p>
+      )}
+    </section>
+  );
+}
diff --git a/components/project/DeleteProjectButton.tsx b/components/project/DeleteProjectButton.tsx
new file mode 100644
index 0000000..fe8f66f
--- /dev/null
+++ b/components/project/DeleteProjectButton.tsx
@@ -0,0 +1,51 @@
+'use client';
+
+import { useState } from 'react';
+import { useRouter } from 'next/navigation';
+
+export function DeleteProjectButton({ projectId }: { projectId: number }) {
+  const router = useRouter();
+  const [busy, setBusy] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  async function onDelete() {
+    if (
+      !window.confirm('プロジェクトを削除しますか？この操作は取り消せません。')
+    ) {
+      return;
+    }
+    setBusy(true);
+    setError(null);
+    const res = await fetch(`/api/projects/${projectId}`, {
+      method: 'DELETE',
+    });
+    setBusy(false);
+    if (res.ok) {
+      router.push('/dashboard');
+      router.refresh();
+    } else {
+      const body = (await res.json().catch(() => null)) as {
+        error?: { message?: string };
+      } | null;
+      setError(body?.error?.message ?? '削除に失敗しました');
+    }
+  }
+
+  return (
+    <div className="mt-3">
+      <button
+        type="button"
+        onClick={onDelete}
+        disabled={busy}
+        className="rounded bg-red-600 px-4 py-2 text-sm font-medium text-white hover:bg-red-700 disabled:opacity-50"
+      >
+        {busy ? '削除中...' : 'プロジェクトを削除'}
+      </button>
+      {error && (
+        <p className="mt-2 text-sm text-red-600" role="alert">
+          {error}
+        </p>
+      )}
+    </div>
+  );
+}
diff --git a/components/project/ProjectCard.tsx b/components/project/ProjectCard.tsx
new file mode 100644
index 0000000..29388d2
--- /dev/null
+++ b/components/project/ProjectCard.tsx
@@ -0,0 +1,40 @@
+import type { Project } from '@/lib/types';
+
+const STATUS_LABELS: Record<string, string> = {
+  active: 'Active',
+  on_hold: 'On Hold',
+  completed: 'Completed',
+  archived: 'Archived',
+};
+
+const STATUS_COLORS: Record<string, string> = {
+  active: 'bg-green-100 text-green-800',
+  on_hold: 'bg-yellow-100 text-yellow-800',
+  completed: 'bg-blue-100 text-blue-800',
+  archived: 'bg-gray-200 text-gray-700',
+};
+
+export function ProjectCard({ project }: { project: Project }) {
+  return (
+    <a
+      href={`/projects/${project.id}`}
+      className="block rounded-lg border bg-white p-4 shadow-sm transition hover:shadow-md"
+    >
+      <div className="flex items-center justify-between">
+        <h3 className="font-semibold text-gray-800">{project.name}</h3>
+        <span
+          className={`rounded px-2 py-0.5 text-xs ${
+            STATUS_COLORS[project.status] ?? 'bg-gray-100 text-gray-700'
+          }`}
+        >
+          {STATUS_LABELS[project.status] ?? project.status}
+        </span>
+      </div>
+      {project.description && (
+        <p className="mt-2 line-clamp-2 text-sm text-gray-600">
+          {project.description}
+        </p>
+      )}
+    </a>
+  );
+}
diff --git a/components/project/ProjectSettingsForm.tsx b/components/project/ProjectSettingsForm.tsx
new file mode 100644
index 0000000..b848733
--- /dev/null
+++ b/components/project/ProjectSettingsForm.tsx
@@ -0,0 +1,120 @@
+'use client';
+
+import { useState, type FormEvent } from 'react';
+import { useRouter } from 'next/navigation';
+import type { Project } from '@/lib/types';
+
+export function ProjectSettingsForm({
+  project,
+  canManage,
+}: {
+  project: Project;
+  canManage: boolean;
+}) {
+  const router = useRouter();
+  const [name, setName] = useState(project.name);
+  const [description, setDescription] = useState(project.description ?? '');
+  const [status, setStatus] = useState(project.status);
+  const [error, setError] = useState<string | null>(null);
+  const [saved, setSaved] = useState(false);
+  const [loading, setLoading] = useState(false);
+
+  async function onSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setLoading(true);
+    setError(null);
+    setSaved(false);
+
+    const res = await fetch(`/api/projects/${project.id}`, {
+      method: 'PATCH',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        name,
+        description: description || undefined,
+        status,
+      }),
+    });
+
+    setLoading(false);
+    if (res.ok) {
+      setSaved(true);
+      router.refresh();
+    } else {
+      const body = (await res.json().catch(() => null)) as {
+        error?: { message?: string };
+      } | null;
+      setError(body?.error?.message ?? '更新に失敗しました');
+    }
+  }
+
+  if (!canManage) {
+    return (
+      <p className="text-sm text-gray-500">
+        プロジェクトの設定変更には管理者権限が必要です。
+      </p>
+    );
+  }
+
+  return (
+    <form onSubmit={onSubmit} className="space-y-4">
+      <div>
+        <label htmlFor="name" className="block text-sm font-medium">
+          プロジェクト名
+        </label>
+        <input
+          id="name"
+          type="text"
+          value={name}
+          onChange={(e) => setName(e.target.value)}
+          className="mt-1 w-full rounded border px-3 py-2"
+        />
+      </div>
+      <div>
+        <label htmlFor="description" className="block text-sm font-medium">
+          説明
+        </label>
+        <textarea
+          id="description"
+          value={description}
+          onChange={(e) => setDescription(e.target.value)}
+          className="mt-1 w-full rounded border px-3 py-2"
+        />
+      </div>
+      <div>
+        <label htmlFor="status" className="block text-sm font-medium">
+          ステータス
+        </label>
+        <select
+          id="status"
+          value={status}
+          onChange={(e) =>
+            setStatus(
+              e.target.value as 'active' | 'on_hold' | 'completed' | 'archived'
+            )
+          }
+          className="mt-1 rounded border px-3 py-2"
+        >
+          <option value="active">active</option>
+          <option value="on_hold">on_hold</option>
+          <option value="completed">completed</option>
+          <option value="archived">archived</option>
+        </select>
+      </div>
+      {error && (
+        <p className="text-sm text-red-600" role="alert">
+          {error}
+        </p>
+      )}
+      {saved && (
+        <p className="text-sm text-green-600">プロジェクトを更新しました</p>
+      )}
+      <button
+        type="submit"
+        disabled={loading}
+        className="rounded bg-blue-600 px-4 py-2 font-medium text-white hover:bg-blue-700 disabled:opacity-50"
+      >
+        {loading ? '保存中...' : '保存'}
+      </button>
+    </form>
+  );
+}
diff --git a/components/project/RemoveMemberButton.tsx b/components/project/RemoveMemberButton.tsx
new file mode 100644
index 0000000..ff53a3d
--- /dev/null
+++ b/components/project/RemoveMemberButton.tsx
@@ -0,0 +1,41 @@
+'use client';
+
+import { useState } from 'react';
+import { useRouter } from 'next/navigation';
+
+export function RemoveMemberButton({
+  projectId,
+  userId,
+  label,
+  disabled = false,
+}: {
+  projectId: number;
+  userId: number;
+  label: string;
+  disabled?: boolean;
+}) {
+  const router = useRouter();
+  const [busy, setBusy] = useState(false);
+
+  async function onRemove() {
+    setBusy(true);
+    const res = await fetch(`/api/projects/${projectId}/members/${userId}`, {
+      method: 'DELETE',
+    });
+    setBusy(false);
+    if (res.ok) {
+      router.refresh();
+    }
+  }
+
+  return (
+    <button
+      type="button"
+      onClick={onRemove}
+      disabled={disabled || busy}
+      className="text-xs text-red-600 hover:underline disabled:opacity-50"
+    >
+      {busy ? '削除中...' : label}
+    </button>
+  );
+}
diff --git a/lib/api/services.ts b/lib/api/services.ts
new file mode 100644
index 0000000..6e997a9
--- /dev/null
+++ b/lib/api/services.ts
@@ -0,0 +1,24 @@
+import { getDb } from '@/lib/db/sqlite';
+import { ProjectRepository } from '@/repositories/ProjectRepository';
+import { ProjectMemberRepository } from '@/repositories/ProjectMemberRepository';
+import { NotificationRepository } from '@/repositories/NotificationRepository';
+import { UserRepository } from '@/repositories/UserRepository';
+import { ProjectService } from '@/services/ProjectService';
+
+/**
+ * Route Handler用に各Repository/Serviceを構築するファクトリ。
+ * 依存はすべて同じgetDb()接続を共有し、トランザクション境界を機能させる。
+ */
+export function createProjectService(): ProjectService {
+  const db = getDb();
+  return new ProjectService(
+    new ProjectRepository(db),
+    new ProjectMemberRepository(db),
+    new NotificationRepository(db),
+    db
+  );
+}
+
+export function createUserRepository(): UserRepository {
+  return new UserRepository(getDb());
+}
diff --git a/lib/validators/projectValidator.ts b/lib/validators/projectValidator.ts
new file mode 100644
index 0000000..b47592e
--- /dev/null
+++ b/lib/validators/projectValidator.ts
@@ -0,0 +1,66 @@
+import { ValidationError } from '@/lib/errors';
+import type { ProjectStatus } from '@/lib/types';
+
+const MAX_NAME_LENGTH = 200;
+const MAX_DESCRIPTION_LENGTH = 2000;
+const VALID_STATUSES: ProjectStatus[] = [
+  'active',
+  'on_hold',
+  'completed',
+  'archived',
+];
+
+export interface ProjectCreateInput {
+  name: string;
+  description?: string;
+}
+
+export interface ProjectUpdateInput {
+  name?: string;
+  description?: string;
+  status?: ProjectStatus;
+}
+
+export function validateProjectCreate(input: ProjectCreateInput): void {
+  if (!input.name || !input.name.trim()) {
+    throw new ValidationError('プロジェクト名を入力してください', 'name');
+  }
+  if (input.name.length > MAX_NAME_LENGTH) {
+    throw new ValidationError(
+      `プロジェクト名は${MAX_NAME_LENGTH}文字以内で入力してください`,
+      'name'
+    );
+  }
+  if (input.description && input.description.length > MAX_DESCRIPTION_LENGTH) {
+    throw new ValidationError(
+      `説明文は${MAX_DESCRIPTION_LENGTH}文字以内で入力してください`,
+      'description'
+    );
+  }
+}
+
+export function validateProjectUpdate(input: ProjectUpdateInput): void {
+  if (input.name !== undefined) {
+    if (!input.name.trim()) {
+      throw new ValidationError('プロジェクト名を入力してください', 'name');
+    }
+    if (input.name.length > MAX_NAME_LENGTH) {
+      throw new ValidationError(
+        `プロジェクト名は${MAX_NAME_LENGTH}文字以内で入力してください`,
+        'name'
+      );
+    }
+  }
+  if (
+    input.description !== undefined &&
+    input.description.length > MAX_DESCRIPTION_LENGTH
+  ) {
+    throw new ValidationError(
+      `説明文は${MAX_DESCRIPTION_LENGTH}文字以内で入力してください`,
+      'description'
+    );
+  }
+  if (input.status !== undefined && !VALID_STATUSES.includes(input.status)) {
+    throw new ValidationError('無効なステータスです', 'status');
+  }
+}
diff --git a/playwright.config.ts b/playwright.config.ts
index f3bf3d2..37f4716 100644
--- a/playwright.config.ts
+++ b/playwright.config.ts
@@ -2,6 +2,7 @@ import { defineConfig, devices } from '@playwright/test';
 
 export default defineConfig({
   testDir: './tests/e2e',
+  timeout: 60_000,
   fullyParallel: true,
   forbidOnly: !!process.env.CI,
   retries: process.env.CI ? 2 : 0,
diff --git a/repositories/NotificationRepository.ts b/repositories/NotificationRepository.ts
new file mode 100644
index 0000000..3ba8076
--- /dev/null
+++ b/repositories/NotificationRepository.ts
@@ -0,0 +1,45 @@
+import type { SqliteDatabase } from '@/lib/db/sqlite';
+import type { Notification, NotificationType } from '@/lib/types';
+
+export interface CreateNotificationInput {
+  userId: number;
+  projectId: number | null;
+  type: NotificationType;
+  title: string;
+  body: string | null;
+}
+
+/**
+ * notificationsテーブルへのデータアクセスを担うRepository。
+ * M4ではメンバー追加通知のために create のみ実装する。
+ * 一覧取得・既読化は M5 で拡張する。
+ */
+export class NotificationRepository {
+  constructor(private readonly db: SqliteDatabase) {}
+
+  create(input: CreateNotificationInput): Notification {
+    const now = new Date().toISOString();
+    const result = this.db.execute(
+      `INSERT INTO notifications (user_id, project_id, type, title, body, read_at, created_at)
+       VALUES (@userId, @projectId, @type, @title, @body, NULL, @createdAt)`,
+      {
+        userId: input.userId,
+        projectId: input.projectId,
+        type: input.type,
+        title: input.title,
+        body: input.body,
+        createdAt: now,
+      }
+    );
+    return {
+      id: Number(result.lastInsertRowid),
+      userId: input.userId,
+      projectId: input.projectId,
+      type: input.type,
+      title: input.title,
+      body: input.body,
+      readAt: null,
+      createdAt: now,
+    };
+  }
+}
diff --git a/repositories/ProjectMemberRepository.ts b/repositories/ProjectMemberRepository.ts
new file mode 100644
index 0000000..eca3ce3
--- /dev/null
+++ b/repositories/ProjectMemberRepository.ts
@@ -0,0 +1,123 @@
+import type { SqliteDatabase } from '@/lib/db/sqlite';
+import type {
+  ProjectMember,
+  ProjectMemberRole,
+  User,
+  UserRole,
+  UserStatus,
+} from '@/lib/types';
+
+interface ProjectMemberRow {
+  id: number;
+  project_id: number;
+  user_id: number;
+  role: string;
+  joined_at: string;
+}
+
+interface MemberWithUserRow extends ProjectMemberRow {
+  name: string;
+  email: string;
+  avatar_url: string | null;
+  user_role: string;
+  user_status: string;
+}
+
+export interface ProjectMemberWithUser extends ProjectMember {
+  user: Pick<User, 'id' | 'name' | 'email' | 'avatarUrl' | 'role' | 'status'>;
+}
+
+function mapMember(row: ProjectMemberRow): ProjectMember {
+  return {
+    id: row.id,
+    projectId: row.project_id,
+    userId: row.user_id,
+    role: row.role as ProjectMemberRole,
+    joinedAt: row.joined_at,
+  };
+}
+
+function mapMemberWithUser(row: MemberWithUserRow): ProjectMemberWithUser {
+  return {
+    ...mapMember(row),
+    user: {
+      id: row.user_id,
+      name: row.name,
+      email: row.email,
+      avatarUrl: row.avatar_url,
+      role: row.user_role as UserRole,
+      status: row.user_status as UserStatus,
+    },
+  };
+}
+
+/**
+ * project_membersテーブルへのデータアクセスを担うRepository。
+ */
+export class ProjectMemberRepository {
+  constructor(private readonly db: SqliteDatabase) {}
+
+  findByProject(projectId: number): ProjectMemberWithUser[] {
+    const rows = this.db.query<MemberWithUserRow>(
+      `SELECT pm.*, u.name, u.email, u.avatar_url, u.role AS user_role, u.status AS user_status
+       FROM project_members pm
+       INNER JOIN users u ON u.id = pm.user_id
+       WHERE pm.project_id = @projectId
+       ORDER BY pm.id`,
+      { projectId }
+    );
+    return rows.map(mapMemberWithUser);
+  }
+
+  findByUser(userId: number): ProjectMember[] {
+    const rows = this.db.query<ProjectMemberRow>(
+      'SELECT * FROM project_members WHERE user_id = @userId ORDER BY id',
+      { userId }
+    );
+    return rows.map(mapMember);
+  }
+
+  add(
+    projectId: number,
+    userId: number,
+    role: ProjectMemberRole
+  ): ProjectMember {
+    const now = new Date().toISOString();
+    const result = this.db.execute(
+      `INSERT INTO project_members (project_id, user_id, role, joined_at)
+       VALUES (@projectId, @userId, @role, @joinedAt)`,
+      { projectId, userId, role, joinedAt: now }
+    );
+    return {
+      id: Number(result.lastInsertRowid),
+      projectId,
+      userId,
+      role,
+      joinedAt: now,
+    };
+  }
+
+  remove(projectId: number, userId: number): boolean {
+    const result = this.db.execute(
+      'DELETE FROM project_members WHERE project_id = @projectId AND user_id = @userId',
+      { projectId, userId }
+    );
+    return result.changes > 0;
+  }
+
+  isMember(projectId: number, userId: number): boolean {
+    const row = this.db.get<{ id: number }>(
+      'SELECT id FROM project_members WHERE project_id = @projectId AND user_id = @userId',
+      { projectId, userId }
+    );
+    return row !== null;
+  }
+
+  getRole(projectId: number, userId: number): ProjectMemberRole | null {
+    const row = this.db.get<{ role: string }>(
+      'SELECT role FROM project_members WHERE project_id = @projectId AND user_id = @userId',
+      { projectId, userId }
+    );
+    return row ? (row.role as ProjectMemberRole) : null;
+  }
+}
diff --git a/repositories/ProjectRepository.ts b/repositories/ProjectRepository.ts
new file mode 100644
index 0000000..199dda3
--- /dev/null
+++ b/repositories/ProjectRepository.ts
@@ -0,0 +1,126 @@
+import type { SqliteDatabase } from '@/lib/db/sqlite';
+import type { Project, ProjectStatus } from '@/lib/types';
+
+interface ProjectRow {
+  id: number;
+  name: string;
+  description: string | null;
+  status: string;
+  owner_id: number;
+  created_at: string;
+  updated_at: string;
+}
+
+function mapProject(row: ProjectRow): Project {
+  return {
+    id: row.id,
+    name: row.name,
+    description: row.description,
+    status: row.status as ProjectStatus,
+    ownerId: row.owner_id,
+    createdAt: row.created_at,
+    updatedAt: row.updated_at,
+  };
+}
+
+export interface CreateProjectInput {
+  name: string;
+  description?: string;
+  ownerId: number;
+}
+
+export interface UpdateProjectInput {
+  name?: string;
+  description?: string | null;
+  status?: ProjectStatus;
+}
+
+/**
+ * projectsテーブルへのデータアクセスを担うRepository。
+ */
+export class ProjectRepository {
+  constructor(private readonly db: SqliteDatabase) {}
+
+  findById(id: number): Project | null {
+    const row = this.db.get<ProjectRow>(
+      'SELECT * FROM projects WHERE id = @id',
+      { id }
+    );
+    return row ? mapProject(row) : null;
+  }
+
+  findByOwner(ownerId: number): Project[] {
+    const rows = this.db.query<ProjectRow>(
+      'SELECT * FROM projects WHERE owner_id = @ownerId ORDER BY id',
+      { ownerId }
+    );
+    return rows.map(mapProject);
+  }
+
+  /** ユーザーが参加しているプロジェクト一覧を取得する */
+  findProjectsByUserId(userId: number): Project[] {
+    const rows = this.db.query<ProjectRow>(
+      `SELECT p.* FROM projects p
+       INNER JOIN project_members pm ON pm.project_id = p.id
+       WHERE pm.user_id = @userId
+       ORDER BY p.id`,
+      { userId }
+    );
+    return rows.map(mapProject);
+  }
+
+  create(input: CreateProjectInput): Project {
+    const now = new Date().toISOString();
+    const result = this.db.execute(
+      `INSERT INTO projects (name, description, status, owner_id, created_at, updated_at)
+       VALUES (@name, @description, @status, @ownerId, @createdAt, @updatedAt)`,
+      {
+        name: input.name,
+        description: input.description ?? null,
+        status: 'active',
+        ownerId: input.ownerId,
+        createdAt: now,
+        updatedAt: now,
+      }
+    );
+    const created = this.findById(Number(result.lastInsertRowid));
+    if (!created) {
+      throw new Error('Failed to create project');
+    }
+    return created;
+  }
+
+  update(id: number, input: UpdateProjectInput): Project | null {
+    const fields: string[] = ['updated_at = @updatedAt'];
+    const params: Record<string, unknown> = {
+      updatedAt: new Date().toISOString(),
+      id,
+    };
+
+    if (input.name !== undefined) {
+      fields.push('name = @name');
+      params.name = input.name;
+    }
+    if (input.description !== undefined) {
+      fields.push('description = @description');
+      params.description = input.description;
+    }
+    if (input.status !== undefined) {
+      fields.push('status = @status');
+      params.status = input.status;
+    }
+
+    this.db.execute(
+      `UPDATE projects SET ${fields.join(', ')} WHERE id = @id`,
+      params
+    );
+    return this.findById(id);
+  }
+
+  delete(id: number): boolean {
+    const result = this.db.execute('DELETE FROM projects WHERE id = @id', {
+      id,
+    });
+    return result.changes > 0;
+  }
+}
diff --git a/services/ProjectService.ts b/services/ProjectService.ts
new file mode 100644
index 0000000..e956a4c
--- /dev/null
+++ b/services/ProjectService.ts
@@ -0,0 +1,162 @@
+import type { SqliteDatabase } from '@/lib/db/sqlite';
+import { ProjectRepository } from '@/repositories/ProjectRepository';
+import {
+  ProjectMemberRepository,
+  type ProjectMemberWithUser,
+} from '@/repositories/ProjectMemberRepository';
+import { NotificationRepository } from '@/repositories/NotificationRepository';
+import {
+  validateProjectCreate,
+  validateProjectUpdate,
+  type ProjectUpdateInput,
+} from '@/lib/validators/projectValidator';
+import { NotFoundError, ForbiddenError, ConflictError } from '@/lib/errors';
+import type { Project, ProjectMember, ProjectMemberRole } from '@/lib/types';
+
+export interface CreateProjectInput {
+  name: string;
+  description?: string;
+}
+
+export interface ProjectDashboard {
+  project: Project;
+  members: ProjectMemberWithUser[];
+}
+
+/**
+ * プロジェクト・メンバー管理の業務ロジックを担うService。
+ * 権限チェック(isMember/ロール)・トランザクション境界・メンバー追加通知を扱う。
+ */
+export class ProjectService {
+  constructor(
+    private readonly projectRepository: ProjectRepository,
+    private readonly projectMemberRepository: ProjectMemberRepository,
+    private readonly notificationRepository: NotificationRepository,
+    private readonly db: SqliteDatabase
+  ) {}
+
+  createProject(actorId: number, input: CreateProjectInput): Project {
+    validateProjectCreate(input);
+    return this.db.transaction(() => {
+      const project = this.projectRepository.create({
+        name: input.name,
+        description: input.description,
+        ownerId: actorId,
+      });
+      // プロジェクト作成者を管理者(admin)メンバーとして登録
+      this.projectMemberRepository.add(project.id, actorId, 'admin');
+      return project;
+    });
+  }
+
+  getProject(actorId: number, projectId: number): Project {
+    return this.requireProjectMember(projectId, actorId);
+  }
+
+  getMyProjects(userId: number): Project[] {
+    return this.projectRepository.findProjectsByUserId(userId);
+  }
+
+  updateProject(
+    actorId: number,
+    projectId: number,
+    input: ProjectUpdateInput
+  ): Project {
+    validateProjectUpdate(input);
+    this.requireProjectAdmin(projectId, actorId);
+    const updated = this.projectRepository.update(projectId, input);
+    if (!updated) {
+      throw new NotFoundError('Project', projectId);
+    }
+    return updated;
+  }
+
+  archiveProject(actorId: number, projectId: number): Project {
+    this.requireProjectAdmin(projectId, actorId);
+    const updated = this.projectRepository.update(projectId, {
+      status: 'archived',
+    });
+    if (!updated) {
+      throw new NotFoundError('Project', projectId);
+    }
+    return updated;
+  }
+
+  deleteProject(actorId: number, projectId: number): void {
+    this.requireProjectAdmin(projectId, actorId);
+    this.projectRepository.delete(projectId);
+  }
+
+  getMembers(actorId: number, projectId: number): ProjectMemberWithUser[] {
+    this.requireProjectMember(projectId, actorId);
+    return this.projectMemberRepository.findByProject(projectId);
+  }
+
+  /** 操作者のプロジェクト内ロールを取得する（非参加者・非存在プロジェクトは null） */
+  getMemberRole(actorId: number, projectId: number): ProjectMemberRole | null {
+    return this.projectMemberRepository.getRole(projectId, actorId);
+  }
+
+  addMember(
+    actorId: number,
+    projectId: number,
+    userId: number,
+    role: ProjectMemberRole
+  ): ProjectMember {
+    this.requireProjectAdmin(projectId, actorId);
+    if (this.projectMemberRepository.isMember(projectId, userId)) {
+      throw new ConflictError('このユーザーは既にメンバーです');
+    }
+    return this.db.transaction(() => {
+      const member = this.projectMemberRepository.add(projectId, userId, role);
+      // 追加されたユーザーへ通知(M5のNotificationService連携相当を直接記録)
+      this.notificationRepository.create({
+        userId,
+        projectId,
+        type: 'project_added',
+        title: 'プロジェクトに追加されました',
+        body: `プロジェクトID ${projectId} のメンバーに追加されました`,
+      });
+      return member;
+    });
+  }
+
+  removeMember(actorId: number, projectId: number, userId: number): void {
+    this.requireProjectMember(projectId, actorId);
+    const actorRole = this.projectMemberRepository.getRole(projectId, actorId);
+    // 管理者は誰でも削除可能。一般メンバーは自分自身のみ削除可能。
+    if (actorId !== userId && actorRole !== 'admin') {
+      throw new ForbiddenError('他のメンバーの削除には管理者権限が必要です');
+    }
+    const removed = this.projectMemberRepository.remove(projectId, userId);
+    if (!removed) {
+      throw new NotFoundError('Member', userId);
+    }
+  }
+
+  getDashboard(actorId: number, projectId: number): ProjectDashboard {
+    const project = this.requireProjectMember(projectId, actorId);
+    const members = this.projectMemberRepository.findByProject(projectId);
+    return { project, members };
+  }
+
+  private requireProjectMember(projectId: number, actorId: number): Project {
+    const project = this.projectRepository.findById(projectId);
+    if (!project) {
+      throw new NotFoundError('Project', projectId);
+    }
+    if (!this.projectMemberRepository.isMember(projectId, actorId)) {
+      throw new ForbiddenError('プロジェクトに参加していません');
+    }
+    return project;
+  }
+
+  private requireProjectAdmin(projectId: number, actorId: number): Project {
+    const project = this.requireProjectMember(projectId, actorId);
+    const role = this.projectMemberRepository.getRole(projectId, actorId);
+    if (role !== 'admin') {
+      throw new ForbiddenError('プロジェクト管理者権限が必要です');
+    }
+    return project;
+  }
+}
diff --git a/tests/e2e/project-management.spec.ts b/tests/e2e/project-management.spec.ts
new file mode 100644
index 0000000..3efc092
--- /dev/null
+++ b/tests/e2e/project-management.spec.ts
@@ -0,0 +1,125 @@
+import { test, expect } from '@playwright/test';
+
+function unique(prefix: string): string {
+  return `${prefix}-${Date.now()}-${Math.floor(Math.random() * 1_000_000)}`;
+}
+
+async function registerAndLogin(
+  page: import('@playwright/test').Page,
+  email: string
+) {
+  await page.goto('/login');
+  await page.getByRole('button', { name: '新規登録はこちら' }).click();
+  await page.getByLabel('表示名').fill('Owner');
+  await page.getByLabel('メールアドレス').fill(email);
+  await page.getByLabel('パスワード').fill('password123');
+  await page.getByRole('button', { name: '登録する' }).click();
+  await expect(page).toHaveURL(/\/dashboard/);
+}
+
+function extractProjectId(url: string): number {
+  const match = url.match(/\/projects\/(\d+)/);
+  if (!match) throw new Error(`project id not found in ${url}`);
+  return Number(match[1]);
+}
+
+test.describe('project management', () => {
+  test('create a project, add and remove a member, then archive', async ({
+    page,
+    request,
+  }) => {
+    const ownerEmail = unique('owner') + '@example.com';
+    const memberEmail = unique('member') + '@example.com';
+    const projectName = unique('Project');
+
+    // オーナー登録＋ログイン
+    await registerAndLogin(page, ownerEmail);
+
+    // プロジェクト作成(UI)
+    await page.getByLabel('プロジェクト名').fill(projectName);
+    await page.getByRole('button', { name: '新規プロジェクト' }).click();
+    await expect(page).toHaveURL(/\/projects\/\d+$/);
+    await expect(
+      page.getByRole('heading', { name: projectName })
+    ).toBeVisible();
+    const projectId = extractProjectId(page.url());
+
+    // 追加用メンバーを事前登録
+    await request.post('/api/auth/register', {
+      data: {
+        name: 'Member User',
+        email: memberEmail,
+        password: 'password123',
+      },
+    });
+
+    // メンバー追加(オーナーのセッションでAPI呼び出し)
+    const addRes = await page.request.post(
+      `/api/projects/${projectId}/members`,
+      { data: { email: memberEmail, role: 'member' } }
+    );
+    expect(addRes.ok()).toBeTruthy();
+    const { member } = (await addRes.json()) as {
+      member: { userId: number };
+    };
+
+    // メンバー一覧画面に反映されているか検証(UI)
+    await page.goto(`/projects/${projectId}/members`);
+    await expect(page.getByText('Member User')).toBeVisible();
+
+    // メンバー削除(API) → 一覧から消えるか検証(UI)
+    const delRes = await page.request.delete(
+      `/api/projects/${projectId}/members/${member.userId}`
+    );
+    expect(delRes.ok()).toBeTruthy();
+    await page.reload();
+    await expect(page.getByText('Member User')).toHaveCount(0);
+
+    // アーカイブ(API) → 概要画面に反映されているか検証(UI)
+    const archiveRes = await page.request.patch(`/api/projects/${projectId}`, {
+      data: { status: 'archived' },
+    });
+    expect(archiveRes.ok()).toBeTruthy();
+    await page.goto(`/projects/${projectId}`);
+    await expect(page.getByText('Archived')).toBeVisible();
+  });
+
+  test('non-member cannot access a project they do not belong to', async ({
+    browser,
+    request,
+  }) => {
+    const ownerEmail = unique('owner') + '@example.com';
+    const outsiderEmail = unique('outsider') + '@example.com';
+
+    // オーナーがプロジェクトを作成
+    const ownerContext = await browser.newContext();
+    const ownerPage = await ownerContext.newPage();
+    await registerAndLogin(ownerPage, ownerEmail);
+    await ownerPage.getByLabel('プロジェクト名').fill(unique('Secret'));
+    await ownerPage.getByRole('button', { name: '新規プロジェクト' }).click();
+    const projectUrl = ownerPage.url();
+
+    // 外部ユーザーは登録のみ（プロジェクト非参加）
+    await request.post('/api/auth/register', {
+      data: {
+        name: 'Outsider',
+        email: outsiderEmail,
+        password: 'password123',
+      },
+    });
+    const outsiderContext = await browser.newContext();
+    const outsiderPage = await outsiderContext.newPage();
+    await outsiderPage.goto('/login');
+    await outsiderPage.getByLabel('メールアドレス').fill(outsiderEmail);
+    await outsiderPage.getByLabel('パスワード').fill('password123');
+    await outsiderPage.getByRole('button', { name: 'ログイン' }).click();
+    await expect(outsiderPage).toHaveURL(/\/dashboard/);
+
+    // プロジェクト詳細へ直接アクセス → ダッシュボードへリダイレクト
+    await outsiderPage.goto(projectUrl);
+    await expect(outsiderPage).toHaveURL(/\/dashboard$/);
+
+    await ownerContext.close();
+    await outsiderContext.close();
+  });
+});
diff --git a/tests/integration/project-member-permission.test.ts b/tests/integration/project-member-permission.test.ts
new file mode 100644
index 0000000..4f60b07
--- /dev/null
+++ b/tests/integration/project-member-permission.test.ts
@@ -0,0 +1,99 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { createMigratedTestDb } from '@/tests/helpers/db';
+import type { SqliteDatabase } from '@/lib/db/sqlite';
+import { UserRepository } from '@/repositories/UserRepository';
+import { ProjectRepository } from '@/repositories/ProjectRepository';
+import { ProjectMemberRepository } from '@/repositories/ProjectMemberRepository';
+import { NotificationRepository } from '@/repositories/NotificationRepository';
+import { ProjectService } from '@/services/ProjectService';
+import { ForbiddenError } from '@/lib/errors';
+
+describe('project member permission (integration)', () => {
+  let db: SqliteDatabase;
+  let userRepo: UserRepository;
+  let service: ProjectService;
+  let ownerA: number;
+  let memberB: number;
+  let outsiderC: number;
+
+  beforeEach(() => {
+    db = createMigratedTestDb();
+    userRepo = new UserRepository(db);
+    service = new ProjectService(
+      new ProjectRepository(db),
+      new ProjectMemberRepository(db),
+      new NotificationRepository(db),
+      db
+    );
+
+    ownerA = userRepo.create({
+      name: 'A',
+      email: 'a@example.com',
+      passwordHash: 'h',
+    }).id;
+    memberB = userRepo.create({
+      name: 'B',
+      email: 'b@example.com',
+      passwordHash: 'h',
+    }).id;
+    outsiderC = userRepo.create({
+      name: 'C',
+      email: 'c@example.com',
+      passwordHash: 'h',
+    }).id;
+  });
+
+  afterEach(() => {
+    db.close();
+  });
+
+  it('non-members cannot access any project data; members can', () => {
+    const p1 = service.createProject(ownerA, { name: 'P1' });
+    service.addMember(ownerA, p1.id, memberB, 'member');
+
+    // メンバー B はアクセス可能
+    expect(() => service.getProject(memberB, p1.id)).not.toThrow();
+    expect(() => service.getDashboard(memberB, p1.id)).not.toThrow();
+    expect(service.getMembers(memberB, p1.id).length).toBeGreaterThan(0);
+
+    // 非メンバー C はすべて拒否
+    expect(() => service.getProject(outsiderC, p1.id)).toThrow(ForbiddenError);
+    expect(() => service.getDashboard(outsiderC, p1.id)).toThrow(
+      ForbiddenError
+    );
+    expect(() => service.getMembers(outsiderC, p1.id)).toThrow(ForbiddenError);
+  });
+
+  it('a member of one project cannot access another project', () => {
+    const p1 = service.createProject(ownerA, { name: 'P1' });
+    const p2 = service.createProject(ownerA, { name: 'P2' });
+    service.addMember(ownerA, p1.id, memberB, 'member');
+
+    // B は P1 のメンバーだが P2 には非参加
+    expect(() => service.getProject(memberB, p2.id)).toThrow(ForbiddenError);
+  });
+
+  it('a non-admin member cannot manage members or edit the project', () => {
+    const p1 = service.createProject(ownerA, { name: 'P1' });
+    service.addMember(ownerA, p1.id, memberB, 'member');
+
+    expect(() =>
+      service.updateProject(memberB, p1.id, { name: 'hacked' })
+    ).toThrow(ForbiddenError);
+    expect(() =>
+      service.addMember(memberB, p1.id, outsiderC, 'member')
+    ).toThrow(ForbiddenError);
+    expect(() => service.archiveProject(memberB, p1.id)).toThrow(
+      ForbiddenError
+    );
+  });
+
+  it('getMyProjects only returns projects the user belongs to', () => {
+    const p1 = service.createProject(ownerA, { name: 'P1' });
+    service.createProject(ownerA, { name: 'P2' });
+    service.addMember(ownerA, p1.id, memberB, 'member');
+
+    const projectsForB = service.getMyProjects(memberB);
+    expect(projectsForB.map((p) => p.id)).toEqual([p1.id]);
+  });
+});
diff --git a/tests/unit/repositories/ProjectMemberRepository.test.ts b/tests/unit/repositories/ProjectMemberRepository.test.ts
new file mode 100644
index 0000000..82f078d
--- /dev/null
+++ b/tests/unit/repositories/ProjectMemberRepository.test.ts
@@ -0,0 +1,100 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { createMigratedTestDb } from '@/tests/helpers/db';
+import type { SqliteDatabase } from '@/lib/db/sqlite';
+import { UserRepository } from '@/repositories/UserRepository';
+import { ProjectRepository } from '@/repositories/ProjectRepository';
+import { ProjectMemberRepository } from '@/repositories/ProjectMemberRepository';
+
+describe('ProjectMemberRepository', () => {
+  let db: SqliteDatabase;
+  let userRepo: UserRepository;
+  let projectRepo: ProjectRepository;
+  let repo: ProjectMemberRepository;
+  let ownerId: number;
+  let projectId: number;
+
+  beforeEach(() => {
+    db = createMigratedTestDb();
+    userRepo = new UserRepository(db);
+    projectRepo = new ProjectRepository(db);
+    repo = new ProjectMemberRepository(db);
+    ownerId = userRepo.create({
+      name: 'Owner',
+      email: 'owner@example.com',
+      passwordHash: 'h',
+    }).id;
+    projectId = projectRepo.create({ name: 'P', ownerId }).id;
+  });
+
+  afterEach(() => {
+    db.close();
+  });
+
+  describe('add / findByProject', () => {
+    it('adds a member and lists them with user info', () => {
+      repo.add(projectId, ownerId, 'admin');
+
+      const members = repo.findByProject(projectId);
+      expect(members).toHaveLength(1);
+      expect(members[0].userId).toBe(ownerId);
+      expect(members[0].role).toBe('admin');
+      expect(members[0].user.email).toBe('owner@example.com');
+    });
+
+    it('rejects adding the same member twice (UNIQUE constraint)', () => {
+      repo.add(projectId, ownerId, 'admin');
+      expect(() => repo.add(projectId, ownerId, 'member')).toThrow();
+    });
+  });
+
+  describe('isMember', () => {
+    it('returns true for a member and false otherwise', () => {
+      repo.add(projectId, ownerId, 'admin');
+
+      expect(repo.isMember(projectId, ownerId)).toBe(true);
+      expect(repo.isMember(projectId, 99999)).toBe(false);
+    });
+  });
+
+  describe('getRole', () => {
+    it('returns the role for a member', () => {
+      repo.add(projectId, ownerId, 'admin');
+
+      expect(repo.getRole(projectId, ownerId)).toBe('admin');
+    });
+
+    it('returns null for a non-member', () => {
+      expect(repo.getRole(projectId, 99999)).toBeNull();
+    });
+  });
+
+  describe('remove', () => {
+    it('removes a member and returns true', () => {
+      repo.add(projectId, ownerId, 'admin');
+
+      expect(repo.remove(projectId, ownerId)).toBe(true);
+      expect(repo.isMember(projectId, ownerId)).toBe(false);
+    });
+
+    it('returns false when the member does not exist', () => {
+      expect(repo.remove(projectId, 99999)).toBe(false);
+    });
+  });
+
+  describe('findByUser', () => {
+    it('returns memberships for a user across projects', () => {
+      const other = userRepo.create({
+        name: 'Other',
+        email: 'other@example.com',
+        passwordHash: 'h',
+      }).id;
+      const p2 = projectRepo.create({ name: 'P2', ownerId }).id;
+
+      repo.add(projectId, other, 'member');
+      repo.add(p2, other, 'admin');
+
+      const memberships = repo.findByUser(other);
+      expect(memberships).toHaveLength(2);
+    });
+  });
+});
diff --git a/tests/unit/repositories/ProjectRepository.test.ts b/tests/unit/repositories/ProjectRepository.test.ts
new file mode 100644
index 0000000..9e276f6
--- /dev/null
+++ b/tests/unit/repositories/ProjectRepository.test.ts
@@ -0,0 +1,119 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { createMigratedTestDb } from '@/tests/helpers/db';
+import type { SqliteDatabase } from '@/lib/db/sqlite';
+import { UserRepository } from '@/repositories/UserRepository';
+import { ProjectRepository } from '@/repositories/ProjectRepository';
+import { ProjectMemberRepository } from '@/repositories/ProjectMemberRepository';
+
+describe('ProjectRepository', () => {
+  let db: SqliteDatabase;
+  let userRepo: UserRepository;
+  let repo: ProjectRepository;
+  let memberRepo: ProjectMemberRepository;
+  let ownerId: number;
+
+  beforeEach(() => {
+    db = createMigratedTestDb();
+    userRepo = new UserRepository(db);
+    repo = new ProjectRepository(db);
+    memberRepo = new ProjectMemberRepository(db);
+    ownerId = userRepo.create({
+      name: 'Owner',
+      email: 'owner@example.com',
+      passwordHash: 'h',
+    }).id;
+  });
+
+  afterEach(() => {
+    db.close();
+  });
+
+  describe('create', () => {
+    it('creates a project with active status and returns it', () => {
+      const project = repo.create({
+        name: 'Project A',
+        description: 'desc',
+        ownerId,
+      });
+
+      expect(project.id).toBeGreaterThan(0);
+      expect(project.name).toBe('Project A');
+      expect(project.description).toBe('desc');
+      expect(project.status).toBe('active');
+      expect(project.ownerId).toBe(ownerId);
+    });
+  });
+
+  describe('findById', () => {
+    it('returns the project when found', () => {
+      const created = repo.create({ name: 'P', ownerId });
+
+      expect(repo.findById(created.id)?.name).toBe('P');
+    });
+
+    it('returns null when not found', () => {
+      expect(repo.findById(99999)).toBeNull();
+    });
+  });
+
+  describe('findByOwner', () => {
+    it('returns projects owned by the user', () => {
+      repo.create({ name: 'P1', ownerId });
+      repo.create({ name: 'P2', ownerId });
+
+      const owned = repo.findByOwner(ownerId);
+      expect(owned).toHaveLength(2);
+    });
+  });
+
+  describe('findProjectsByUserId', () => {
+    it('returns only projects the user is a member of', () => {
+      const p1 = repo.create({ name: 'P1', ownerId });
+      const p2 = repo.create({ name: 'P2', ownerId });
+      const other = userRepo.create({
+        name: 'Other',
+        email: 'other@example.com',
+        passwordHash: 'h',
+      }).id;
+
+      memberRepo.add(p1.id, other, 'member');
+
+      const projects = repo.findProjectsByUserId(other);
+      expect(projects.map((p) => p.id)).toEqual([p1.id]);
+      expect(projects.map((p) => p.id)).not.toContain(p2.id);
+    });
+  });
+
+  describe('update', () => {
+    it('updates name, description and status', () => {
+      const created = repo.create({ name: 'P', ownerId });
+
+      const updated = repo.update(created.id, {
+        name: 'P2',
+        description: 'new desc',
+        status: 'archived',
+      });
+
+      expect(updated?.name).toBe('P2');
+      expect(updated?.description).toBe('new desc');
+      expect(updated?.status).toBe('archived');
+    });
+
+    it('returns null for a non-existent project', () => {
+      expect(repo.update(99999, { name: 'X' })).toBeNull();
+    });
+  });
+
+  describe('delete', () => {
+    it('deletes the project and returns true', () => {
+      const created = repo.create({ name: 'P', ownerId });
+
+      expect(repo.delete(created.id)).toBe(true);
+      expect(repo.findById(created.id)).toBeNull();
+    });
+
+    it('returns false when the project does not exist', () => {
+      expect(repo.delete(99999)).toBe(false);
+    });
+  });
+});
diff --git a/tests/unit/services/ProjectService.test.ts b/tests/unit/services/ProjectService.test.ts
new file mode 100644
index 0000000..16f62d4
--- /dev/null
+++ b/tests/unit/services/ProjectService.test.ts
@@ -0,0 +1,230 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { createMigratedTestDb } from '@/tests/helpers/db';
+import type { SqliteDatabase } from '@/lib/db/sqlite';
+import { UserRepository } from '@/repositories/UserRepository';
+import { ProjectRepository } from '@/repositories/ProjectRepository';
+import { ProjectMemberRepository } from '@/repositories/ProjectMemberRepository';
+import { NotificationRepository } from '@/repositories/NotificationRepository';
+import { ProjectService } from '@/services/ProjectService';
+import { ForbiddenError, NotFoundError, ConflictError } from '@/lib/errors';
+
+function createService(db: SqliteDatabase) {
+  return new ProjectService(
+    new ProjectRepository(db),
+    new ProjectMemberRepository(db),
+    new NotificationRepository(db),
+    db
+  );
+}
+
+function createUser(repo: UserRepository, email: string, name = 'User') {
+  return repo.create({ name, email, passwordHash: 'hash' });
+}
+
+describe('ProjectService', () => {
+  let db: SqliteDatabase;
+  let userRepo: UserRepository;
+  let service: ProjectService;
+  let ownerId: number;
+
+  beforeEach(() => {
+    db = createMigratedTestDb();
+    userRepo = new UserRepository(db);
+    service = createService(db);
+    ownerId = createUser(userRepo, 'owner@example.com', 'Owner').id;
+  });
+
+  afterEach(() => {
+    db.close();
+  });
+
+  describe('createProject', () => {
+    it('creates the project and registers the owner as an admin member', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+
+      expect(project.name).toBe('P1');
+      expect(project.ownerId).toBe(ownerId);
+
+      const dashboard = service.getDashboard(ownerId, project.id);
+      expect(dashboard.members).toHaveLength(1);
+      expect(dashboard.members[0].role).toBe('admin');
+      expect(service.getMemberRole(ownerId, project.id)).toBe('admin');
+    });
+  });
+
+  describe('getMyProjects', () => {
+    it('lists projects the user participates in', () => {
+      service.createProject(ownerId, { name: 'P1' });
+      service.createProject(ownerId, { name: 'P2' });
+
+      const projects = service.getMyProjects(ownerId);
+      expect(projects).toHaveLength(2);
+    });
+  });
+
+  describe('updateProject', () => {
+    it('allows an admin to update the project', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+
+      const updated = service.updateProject(ownerId, project.id, {
+        name: 'P1-updated',
+        status: 'on_hold',
+      });
+
+      expect(updated.name).toBe('P1-updated');
+      expect(updated.status).toBe('on_hold');
+    });
+
+    it('forbids a non-admin member from updating', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const member = createUser(userRepo, 'member@example.com').id;
+      service.addMember(ownerId, project.id, member, 'member');
+
+      expect(() =>
+        service.updateProject(member, project.id, { name: 'X' })
+      ).toThrow(ForbiddenError);
+    });
+
+    it('forbids a non-member from updating', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const outsider = createUser(userRepo, 'out@example.com').id;
+
+      expect(() =>
+        service.updateProject(outsider, project.id, { name: 'X' })
+      ).toThrow(ForbiddenError);
+    });
+
+    it('throws NotFoundError for a non-existent project', () => {
+      expect(() =>
+        service.updateProject(ownerId, 99999, { name: 'X' })
+      ).toThrow(NotFoundError);
+    });
+  });
+
+  describe('archiveProject', () => {
+    it('sets the project status to archived', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+
+      const archived = service.archiveProject(ownerId, project.id);
+
+      expect(archived.status).toBe('archived');
+    });
+  });
+
+  describe('deleteProject', () => {
+    it('deletes the project when the actor is an admin', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+
+      service.deleteProject(ownerId, project.id);
+
+      expect(() => service.getProject(ownerId, project.id)).toThrow(
+        NotFoundError
+      );
+    });
+  });
+
+  describe('addMember', () => {
+    it('adds a member and creates a project_added notification', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const newMember = createUser(userRepo, 'new@example.com').id;
+
+      service.addMember(ownerId, project.id, newMember, 'member');
+
+      expect(service.getMemberRole(newMember, project.id)).toBe('member');
+      const notifications = db.query<{
+        id: number;
+        type: string;
+        user_id: number;
+      }>(
+        'SELECT id, type, user_id FROM notifications WHERE user_id = @userId',
+        { userId: newMember }
+      );
+      expect(notifications).toHaveLength(1);
+      expect(notifications[0].type).toBe('project_added');
+    });
+
+    it('rejects adding an existing member with ConflictError', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const newMember = createUser(userRepo, 'new@example.com').id;
+      service.addMember(ownerId, project.id, newMember, 'member');
+
+      expect(() =>
+        service.addMember(ownerId, project.id, newMember, 'member')
+      ).toThrow(ConflictError);
+    });
+
+    it('forbids a non-admin from adding members', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const member = createUser(userRepo, 'member@example.com').id;
+      service.addMember(ownerId, project.id, member, 'member');
+      const target = createUser(userRepo, 'target@example.com').id;
+
+      expect(() =>
+        service.addMember(member, project.id, target, 'member')
+      ).toThrow(ForbiddenError);
+    });
+  });
+
+  describe('removeMember', () => {
+    it('allows an admin to remove another member', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const member = createUser(userRepo, 'member@example.com').id;
+      service.addMember(ownerId, project.id, member, 'member');
+
+      service.removeMember(ownerId, project.id, member);
+
+      expect(service.getMemberRole(member, project.id)).toBeNull();
+    });
+
+    it('allows a member to remove themselves', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const member = createUser(userRepo, 'member@example.com').id;
+      service.addMember(ownerId, project.id, member, 'member');
+
+      service.removeMember(member, project.id, member);
+
+      expect(service.getMemberRole(member, project.id)).toBeNull();
+    });
+
+    it('forbids a member from removing another member', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const member1 = createUser(userRepo, 'm1@example.com').id;
+      const member2 = createUser(userRepo, 'm2@example.com').id;
+      service.addMember(ownerId, project.id, member1, 'member');
+      service.addMember(ownerId, project.id, member2, 'member');
+
+      expect(() => service.removeMember(member1, project.id, member2)).toThrow(
+        ForbiddenError
+      );
+    });
+  });
+
+  describe('getDashboard / getProject', () => {
+    it('returns the project and members for a member', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+
+      const dashboard = service.getDashboard(ownerId, project.id);
+      expect(dashboard.project.id).toBe(project.id);
+      expect(dashboard.members).toHaveLength(1);
+    });
+
+    it('forbids a non-member from accessing the project (isolation)', () => {
+      const project = service.createProject(ownerId, { name: 'P1' });
+      const outsider = createUser(userRepo, 'out@example.com').id;
+
+      expect(() => service.getProject(outsider, project.id)).toThrow(
+        ForbiddenError
+      );
+      expect(() => service.getDashboard(outsider, project.id)).toThrow(
+        ForbiddenError
+      );
+      expect(() => service.getMembers(outsider, project.id)).toThrow(
+        ForbiddenError
+      );
+    });
+
+    it('throws NotFoundError for a non-existent project', () => {
+      expect(() => service.getProject(ownerId, 99999)).toThrow(NotFoundError);
+    });
+  });
+});