diff --git a/src/app/components/ProjectForm.tsx b/src/app/components/ProjectForm.tsx
index 2c2ae11..6898f0f 100644
--- a/src/app/components/ProjectForm.tsx
+++ b/src/app/components/ProjectForm.tsx
@@ -21,21 +21,20 @@ export function ProjectForm({
   onSubmit: (value: ProjectWriteRequest) => void;
 }) {
   const options = useProjectOptions(yearId);
-  const [name, setName] = useState(project?.name ?? '');
-  const [summary, setSummary] = useState(project?.summary ?? '');
-  const [repository, setRepository] = useState(project?.repository ?? '');
-  const [kind, setKind] = useState<ProjectWriteRequest['kind']>(
-    claim ? 'project' : (project?.kind ?? 'project'),
-  );
-  const [groupId, setGroupId] = useState(project?.group?.id ?? '');
-  const [memberIds, setMemberIds] = useState(project?.members.map(({id}) => id) ?? []);
+  const initial = initialValues(project, claim);
+  const [name, setName] = useState(initial.name);
+  const [summary, setSummary] = useState(initial.summary);
+  const [repository, setRepository] = useState(initial.repository);
+  const [kind, setKind] = useState<ProjectWriteRequest['kind']>(initial.kind);
+  const [groupId, setGroupId] = useState(initial.groupId);
+  const [memberIds, setMemberIds] = useState(initial.memberIds);
   const [memberQuery, setMemberQuery] = useState('');
   const [memberResultsOpen, setMemberResultsOpen] = useState(false);
   const [highlightedMember, setHighlightedMember] = useState(-1);
   const memberListboxId = useId();
   const memberSearchId = useId();
-  const [needsHelp, setNeedsHelp] = useState(project?.needsHelp ?? false);
-  const [helpDetails, setHelpDetails] = useState(project?.helpDetails ?? '');
+  const [needsHelp, setNeedsHelp] = useState(initial.needsHelp);
+  const [helpDetails, setHelpDetails] = useState(initial.helpDetails);
 
   useEffect(() => {
     if (!project || claim) return;
@@ -68,6 +67,16 @@ export function ProjectForm({
         .slice(0, 8)
     : [];
   const showMemberResults = memberResultsOpen && Boolean(normalizedMemberQuery);
+  const dirty =
+    name !== initial.name ||
+    summary !== initial.summary ||
+    repository !== initial.repository ||
+    kind !== initial.kind ||
+    groupId !== initial.groupId ||
+    needsHelp !== initial.needsHelp ||
+    helpDetails !== initial.helpDetails ||
+    memberIds.length !== initial.memberIds.length ||
+    memberIds.some((id) => !initial.memberIds.includes(id));
 
   function addMember(id: string) {
     setMemberIds((members) => (members.includes(id) ? members : [...members, id]));
@@ -104,6 +113,11 @@ export function ProjectForm({
     }
   }
 
+  function cancel() {
+    if (dirty && !window.confirm('Discard your unsaved changes to this project?')) return;
+    onCancel();
+  }
+
   function submit(event: FormEvent) {
     event.preventDefault();
     onSubmit({
@@ -327,7 +341,7 @@ export function ProjectForm({
         </p>
       )}
       <div className="formActions">
-        <button type="button" className="textAction" onClick={onCancel}>
+        <button type="button" className="textAction" onClick={cancel}>
           Never mind
         </button>
         <button type="submit" className="primaryAction" disabled={saving}>
@@ -343,3 +357,19 @@ export function ProjectForm({
     </form>
   );
 }
+
+function initialValues(project: ProjectDetail | undefined, claim: boolean) {
+  const kind: ProjectWriteRequest['kind'] = claim
+    ? 'project'
+    : (project?.kind ?? 'project');
+  return {
+    name: project?.name ?? '',
+    summary: project?.summary ?? '',
+    repository: project?.repository ?? '',
+    kind,
+    groupId: project?.group?.id ?? '',
+    memberIds: project?.members.map(({id}) => id) ?? [],
+    needsHelp: project?.needsHelp ?? false,
+    helpDetails: project?.helpDetails ?? '',
+  };
+}
diff --git a/test/app/ProjectForm.test.tsx b/test/app/ProjectForm.test.tsx
index a95fbb8..1dd06fe 100644
--- a/test/app/ProjectForm.test.tsx
+++ b/test/app/ProjectForm.test.tsx
@@ -12,8 +12,13 @@ import type {
 
 const fetchMock = vi.fn<typeof fetch>();
 vi.stubGlobal('fetch', fetchMock);
+const confirmMock = vi.fn<typeof window.confirm>();
+vi.stubGlobal('confirm', confirmMock);
 
-afterEach(() => fetchMock.mockReset());
+afterEach(() => {
+  fetchMock.mockReset();
+  confirmMock.mockReset();
+});
 
 describe('ProjectForm team picker', () => {
   it('filters members by partial name and email', async () => {
@@ -127,12 +132,67 @@ describe('ProjectForm team picker', () => {
   });
 });
 
+describe('ProjectForm cancel confirmation', () => {
+  it('cancels without confirmation when nothing has been edited', async () => {
+    const onCancel = vi.fn();
+    renderProjectForm({project: projectFixture, onCancel});
+
+    await userEvent.click(await screen.findByRole('button', {name: 'Never mind'}));
+
+    expect(confirmMock).not.toHaveBeenCalled();
+    expect(onCancel).toHaveBeenCalledTimes(1);
+  });
+
+  it('keeps the edited form when the discard confirmation is declined', async () => {
+    const onCancel = vi.fn();
+    confirmMock.mockReturnValue(false);
+    renderProjectForm({project: projectFixture, onCancel});
+
+    await userEvent.type(await screen.findByLabelText('Name'), '!');
+    await userEvent.click(screen.getByRole('button', {name: 'Never mind'}));
+
+    expect(confirmMock).toHaveBeenCalledTimes(1);
+    expect(onCancel).not.toHaveBeenCalled();
+    expect(screen.getByLabelText('Name')).toHaveProperty(
+      'value',
+      `${projectFixture.name}!`,
+    );
+  });
+
+  it('cancels an edited form when the discard confirmation is accepted', async () => {
+    const onCancel = vi.fn();
+    confirmMock.mockReturnValue(true);
+    renderProjectForm({project: projectFixture, onCancel});
+
+    await userEvent.type(await screen.findByLabelText('Name'), '!');
+    await userEvent.click(screen.getByRole('button', {name: 'Never mind'}));
+
+    expect(onCancel).toHaveBeenCalledTimes(1);
+  });
+
+  it('confirms before discarding a team change on an otherwise untouched form', async () => {
+    const onCancel = vi.fn();
+    confirmMock.mockReturnValue(false);
+    renderProjectForm({project: projectFixture, onCancel});
+
+    await userEvent.click(
+      await screen.findByRole('button', {name: 'Remove Alice Example from team'}),
+    );
+    await userEvent.click(screen.getByRole('button', {name: 'Never mind'}));
+
+    expect(confirmMock).toHaveBeenCalledTimes(1);
+    expect(onCancel).not.toHaveBeenCalled();
+  });
+});
+
 function renderProjectForm({
   project,
+  onCancel = () => {},
   onSubmit = () => {},
   users = [alice, bob],
 }: {
   project?: ProjectDetail;
+  onCancel?: () => void;
   onSubmit?: (value: ProjectWriteRequest) => void;
   users?: ProjectMember[];
 } = {}) {
@@ -150,7 +210,7 @@ function renderProjectForm({
         project={project}
         saving={false}
         error={null}
-        onCancel={() => {}}
+        onCancel={onCancel}
         onSubmit={onSubmit}
       />
     </QueryClientProvider>,