diff --git a/CHANGELOG.md b/CHANGELOG.md
index 82f4d48..3bfe582 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ what it changes for someone who uses the API. CI checks that it did.
 
 ## Unreleased
 
+- `GET /tasks?done=true` or `?done=false` lists only the tasks that are done, or only those that are not. Any other value of `done` answers 400. (#8)
 - `DELETE /tasks/done` removes every task that is done, and says how many it removed. (#6)
 - `PATCH /tasks/:id` renames a task, body `{"title": "..."}`, and answers with the task. (#5) (#7)
 - `GET /tasks/count` says how many tasks there are, and how many are done.
diff --git a/README.md b/README.md
index 5cf67e9..ac21d3e 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ and in an adopter's first run. It is small on purpose, so a job is cheap and fas
 | Method | Path | What it does |
 |---|---|---|
 | GET | `/health` | Says the server is up |
-| GET | `/tasks` | Lists every task |
+| GET | `/tasks` | Lists every task. Takes `?done=true` or `?done=false` to list only the tasks that are done, or only those that are not |
 | POST | `/tasks` | Adds a task, body `{"title": "..."}` |
 | GET | `/tasks/count` | Says how many tasks there are, and how many are done |
 | DELETE | `/tasks/done` | Removes every task that is done, and says how many |
diff --git a/src/server.ts b/src/server.ts
index 2a46507..5e1b4eb 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -5,7 +5,7 @@ import { TaskList, ValidationError } from './tasks.ts';
  * The HTTP API over a task list:
  *
  *   GET    /health              is the server up
- *   GET    /tasks               every task
+ *   GET    /tasks               every task, or with ?done=true or ?done=false only those that are or are not done
  *   POST   /tasks               add a task, body {"title": "..."}
  *   GET    /tasks/count         how many tasks, and how many are done
  *   DELETE /tasks/done          remove every task that is done, and say how many
@@ -24,7 +24,7 @@ export function createApp(tasks: TaskList = new TaskList()): Server {
 }
 
 async function handle(tasks: TaskList, request: IncomingMessage, response: ServerResponse): Promise<void> {
-  const { pathname } = new URL(request.url ?? '/', 'http://localhost');
+  const { pathname, searchParams } = new URL(request.url ?? '/', 'http://localhost');
   const parts = pathname.split('/').filter(Boolean);
   const method = request.method ?? 'GET';
 
@@ -33,7 +33,7 @@ async function handle(tasks: TaskList, request: IncomingMessage, response: Serve
   if (parts[0] !== 'tasks') return send(response, 404, { error: 'not found' });
 
   if (parts.length === 1) {
-    if (method === 'GET') return send(response, 200, { tasks: tasks.all() });
+    if (method === 'GET') return send(response, 200, { tasks: tasks.all(doneFilter(searchParams)) });
     if (method === 'POST') return send(response, 201, tasks.add((await body(request)).title));
     return send(response, 405, { error: 'method not allowed' });
   }
@@ -59,6 +59,15 @@ function found(response: ServerResponse, task: unknown): void {
   else send(response, 200, task);
 }
 
+/** The `done` query parameter: undefined when it is absent. Throws when it is not exactly one `true` or `false`. */
+function doneFilter(searchParams: URLSearchParams): boolean | undefined {
+  const values = searchParams.getAll('done');
+  if (values.length === 0) return undefined;
+  if (values.length === 1 && values[0] === 'true') return true;
+  if (values.length === 1 && values[0] === 'false') return false;
+  throw new ValidationError('done must be true or false');
+}
+
 async function body(request: IncomingMessage): Promise<Record<string, unknown>> {
   const chunks: Buffer[] = [];
   for await (const chunk of request) chunks.push(chunk as Buffer);
diff --git a/src/tasks.ts b/src/tasks.ts
index 08b1fff..dbddb3f 100644
--- a/src/tasks.ts
+++ b/src/tasks.ts
@@ -17,8 +17,10 @@ export class TaskList {
   private readonly tasks = new Map<number, Task>();
   private nextId = 1;
 
-  all(): Task[] {
-    return [...this.tasks.values()];
+  /** Every task, in the order they were added. Given `done`, only the tasks that are, or are not, done. */
+  all(done?: boolean): Task[] {
+    const tasks = [...this.tasks.values()];
+    return done === undefined ? tasks : tasks.filter((task) => task.done === done);
   }
 
   get(id: number): Task | undefined {
diff --git a/test/server.test.ts b/test/server.test.ts
index 0e2a2fe..1a4eb11 100644
--- a/test/server.test.ts
+++ b/test/server.test.ts
@@ -83,6 +83,61 @@ describe('the HTTP API', () => {
     await call('DELETE', `/tasks/${id}`);
   });
 
+  describe('listing tasks by whether they are done', () => {
+    let first: number;
+    let open: number;
+    let third: number;
+
+    before(async () => {
+      first = (await call('POST', '/tasks', { title: 'Done one' })).json!.id as number;
+      open = (await call('POST', '/tasks', { title: 'Still open' })).json!.id as number;
+      third = (await call('POST', '/tasks', { title: 'Done two' })).json!.id as number;
+      await call('POST', `/tasks/${first}/complete`);
+      await call('POST', `/tasks/${third}/complete`);
+    });
+
+    after(async () => {
+      for (const id of [first, open, third]) await call('DELETE', `/tasks/${id}`);
+    });
+
+    const mine = (json: Record<string, unknown> | undefined) =>
+      (json!.tasks as { id: number }[]).filter((task) => [first, open, third].includes(task.id));
+
+    it('lists only the tasks that are done with ?done=true', async () => {
+      const listed = await call('GET', '/tasks?done=true');
+      assert.equal(listed.status, 200);
+      assert.ok((listed.json!.tasks as { done: boolean }[]).every((task) => task.done));
+      assert.deepEqual(mine(listed.json), [
+        { id: first, title: 'Done one', done: true },
+        { id: third, title: 'Done two', done: true },
+      ]);
+    });
+
+    it('lists only the tasks that are not done with ?done=false', async () => {
+      const listed = await call('GET', '/tasks?done=false');
+      assert.equal(listed.status, 200);
+      assert.ok((listed.json!.tasks as { done: boolean }[]).every((task) => !task.done));
+      assert.deepEqual(mine(listed.json), [{ id: open, title: 'Still open', done: false }]);
+    });
+
+    it('lists every task without done', async () => {
+      const listed = await call('GET', '/tasks');
+      assert.equal(listed.status, 200);
+      assert.deepEqual(mine(listed.json), [
+        { id: first, title: 'Done one', done: true },
+        { id: open, title: 'Still open', done: false },
+        { id: third, title: 'Done two', done: true },
+      ]);
+    });
+
+    it('answers 400 and lists nothing for any other value of done', async () => {
+      const refused = { status: 400, json: { error: 'done must be true or false' } };
+      for (const query of ['done=yes', 'done=1', 'done=TRUE', 'done=', 'done', 'done=true&done=false']) {
+        assert.deepEqual(await call('GET', `/tasks?${query}`), refused, query);
+      }
+    });
+  });
+
   it('refuses a task without a title, and a body that is not JSON', async () => {
     assert.deepEqual(await call('POST', '/tasks', { title: '' }), { status: 400, json: { error: 'title must be text' } });
     assert.deepEqual(await call('POST', '/tasks', 'not json'), { status: 400, json: { error: 'the body must be JSON' } });
diff --git a/test/tasks.test.ts b/test/tasks.test.ts
index 1650aa1..2e0a81a 100644
--- a/test/tasks.test.ts
+++ b/test/tasks.test.ts
@@ -55,6 +55,25 @@ describe('the task list', () => {
     assert.equal(tasks.get(id)?.title, 'Write the spec');
   });
 
+  it('lists only the tasks that are done, or only those that are not, in order', () => {
+    const tasks = new TaskList();
+    assert.deepEqual(tasks.all(true), []);
+    assert.deepEqual(tasks.all(false), []);
+
+    const first = tasks.add('Write the spec');
+    const second = tasks.add('Review it');
+    const third = tasks.add('Ship it');
+    tasks.complete(first.id);
+    tasks.complete(third.id);
+
+    assert.deepEqual(tasks.all(true), [
+      { id: first.id, title: 'Write the spec', done: true },
+      { id: third.id, title: 'Ship it', done: true },
+    ]);
+    assert.deepEqual(tasks.all(false), [{ id: second.id, title: 'Review it', done: false }]);
+    assert.deepEqual(tasks.all().map((task) => task.id), [first.id, second.id, third.id]);
+  });
+
   it('removes a task once', () => {
     const tasks = new TaskList();
     const { id } = tasks.add('Clean up');