diff --git a/src/books/BookDetail.tsx b/src/books/BookDetail.tsx
index 8875c2a..a923019 100644
--- a/src/books/BookDetail.tsx
+++ b/src/books/BookDetail.tsx
@@ -2,6 +2,7 @@ import { useEffect, useState, type FormEvent } from 'react'
 import { Link, useNavigate, useParams } from 'react-router'
 import { api, ApiError, errorMessage, type Book } from '../api'
 import { card, dangerButton, inputClass, labelText, primaryButton, secondaryButton } from '../ui'
+import { NotesJournal } from '../notes/NotesJournal'
 import { ProgressBar, StatusBadge } from './Progress'
 
 export function BookDetail() {
@@ -155,6 +156,7 @@ export function BookDetail() {
           </dialog>
         )}
       </header>
+      <NotesJournal bookId={book.id} />
     </article>
   )
 }
diff --git a/src/notes/NotesJournal.test.tsx b/src/notes/NotesJournal.test.tsx
new file mode 100644
index 0000000..67b31c8
--- /dev/null
+++ b/src/notes/NotesJournal.test.tsx
@@ -0,0 +1,80 @@
+import { screen, within } from '@testing-library/react'
+import { describe, expect, it } from 'vitest'
+import type { Note } from '../api'
+import { dune, renderApp, signedIn } from '../test/helpers'
+
+const older: Note = {
+  id: 11,
+  book_id: 7,
+  body: 'Started reading',
+  created_at: '2026-10-01T10:00:00+00:00',
+  updated_at: '2026-10-01T10:00:00+00:00',
+}
+
+describe('NotesJournal', () => {
+  it('lists entries and adds a new one at the top', async () => {
+    const calls = signedIn({
+      'GET /api/books/7': () => [200, dune],
+      'GET /api/books/7/notes': () => [200, [older]],
+      'POST /api/books/7/notes': ({ body }) => [
+        201,
+        { ...older, id: 12, body: (body as { body: string }).body, created_at: '2026-10-02T10:00:00+00:00', updated_at: '2026-10-02T10:00:00+00:00' },
+      ],
+    })
+    const user = renderApp('/books/7')
+    expect(await screen.findByText('Started reading')).toBeInTheDocument()
+    await user.type(screen.getByLabelText('New journal entry'), 'Loved chapter 3')
+    await user.click(screen.getByRole('button', { name: 'Add entry' }))
+
+    await screen.findByText('Loved chapter 3')
+    const items = screen.getAllByRole('listitem')
+    expect(items[0]).toHaveTextContent('Loved chapter 3')
+    expect(items[1]).toHaveTextContent('Started reading')
+    expect(screen.getByLabelText('New journal entry')).toHaveValue('')
+    expect(calls).toContainEqual({ method: 'POST', path: '/api/books/7/notes', body: { body: 'Loved chapter 3' } })
+  })
+
+  it('edits an entry and marks it edited', async () => {
+    signedIn({
+      'GET /api/books/7': () => [200, dune],
+      'GET /api/books/7/notes': () => [200, [older]],
+      'PATCH /api/notes/11': ({ body }) => [
+        200,
+        { ...older, body: (body as { body: string }).body, updated_at: '2026-10-02T10:00:00+00:00' },
+      ],
+    })
+    const user = renderApp('/books/7')
+    const item = (await screen.findByText('Started reading')).closest('li')!
+    await user.click(within(item).getByRole('button', { name: 'Edit entry' }))
+    const editor = within(item).getByLabelText('Edit entry')
+    await user.clear(editor)
+    await user.type(editor, 'Finished part one')
+    await user.click(within(item).getByRole('button', { name: 'Save' }))
+
+    expect(await within(item).findByText('Finished part one')).toBeInTheDocument()
+    expect(within(item).getByText(/edited/)).toBeInTheDocument()
+  })
+
+  it('deletes an entry', async () => {
+    signedIn({
+      'GET /api/books/7': () => [200, dune],
+      'GET /api/books/7/notes': () => [200, [older]],
+      'DELETE /api/notes/11': () => [204],
+    })
+    const user = renderApp('/books/7')
+    await user.click(await screen.findByRole('button', { name: 'Delete entry' }))
+    expect(await screen.findByText('No entries yet.')).toBeInTheDocument()
+  })
+
+  it('shows the server error when adding fails', async () => {
+    signedIn({
+      'GET /api/books/7': () => [200, dune],
+      'GET /api/books/7/notes': () => [200, []],
+      'POST /api/books/7/notes': () => [400, { error: 'body must be at most 10000 characters', field: 'body' }],
+    })
+    const user = renderApp('/books/7')
+    await user.type(await screen.findByLabelText('New journal entry'), 'x')
+    await user.click(screen.getByRole('button', { name: 'Add entry' }))
+    expect(await screen.findByRole('alert')).toHaveTextContent('body must be at most 10000 characters')
+  })
+})
diff --git a/src/notes/NotesJournal.tsx b/src/notes/NotesJournal.tsx
new file mode 100644
index 0000000..9ddf9ea
--- /dev/null
+++ b/src/notes/NotesJournal.tsx
@@ -0,0 +1,179 @@
+import { useEffect, useState, type FormEvent } from 'react'
+import { api, errorMessage, type Note } from '../api'
+import { card, dangerButton, inputClass, labelText, primaryButton, secondaryButton } from '../ui'
+
+const MAX_NOTE = 10000
+
+export function NotesJournal({ bookId }: { bookId: number }) {
+  const [notes, setNotes] = useState<Note[] | null>(null)
+  const [loadError, setLoadError] = useState<string | null>(null)
+  const [attempt, setAttempt] = useState(0)
+  const [draft, setDraft] = useState('')
+  const [addError, setAddError] = useState<string | null>(null)
+
+  useEffect(() => {
+    let cancelled = false
+    setLoadError(null)
+    api<Note[]>('GET', `/books/${bookId}/notes`).then(
+      (found) => {
+        if (!cancelled) setNotes(found)
+      },
+      (err) => {
+        if (!cancelled) setLoadError(errorMessage(err))
+      },
+    )
+    return () => {
+      cancelled = true
+    }
+  }, [bookId, attempt])
+
+  async function addNote(event: FormEvent) {
+    event.preventDefault()
+    setAddError(null)
+    try {
+      const note = await api<Note>('POST', `/books/${bookId}/notes`, { body: draft })
+      setNotes((prev) => [note, ...(prev ?? [])])
+      setDraft('')
+    } catch (err) {
+      setAddError(errorMessage(err))
+    }
+  }
+
+  return (
+    <section aria-labelledby="journal-heading" className={card}>
+      <h2 id="journal-heading" className="mb-3 text-lg font-semibold">
+        Reading journal
+      </h2>
+      <form onSubmit={addNote} className="space-y-2">
+        <label className="block">
+          <span className={labelText}>New journal entry</span>
+          <textarea
+            className={inputClass}
+            rows={3}
+            maxLength={MAX_NOTE}
+            value={draft}
+            onChange={(e) => setDraft(e.target.value)}
+            required
+            aria-describedby={addError ? 'add-note-error' : undefined}
+          />
+        </label>
+        <button type="submit" className={primaryButton}>
+          Add entry
+        </button>
+        {addError && (
+          <p id="add-note-error" role="alert" className="text-sm text-red-700">
+            {addError}
+          </p>
+        )}
+      </form>
+      {loadError ? (
+        <div role="alert" className="mt-4 flex items-center gap-3 text-red-700">
+          <span>{loadError}</span>
+          <button type="button" className={secondaryButton} onClick={() => setAttempt((n) => n + 1)}>
+            Retry
+          </button>
+        </div>
+      ) : notes === null ? (
+        <p className="mt-4 text-slate-500">Loading…</p>
+      ) : notes.length === 0 ? (
+        <p className="mt-4 text-slate-600">No entries yet.</p>
+      ) : (
+        <ol className="mt-4">
+          {notes.map((note) => (
+            <NoteItem
+              key={note.id}
+              note={note}
+              onSaved={(saved) => setNotes((prev) => prev!.map((n) => (n.id === saved.id ? saved : n)))}
+              onDeleted={() => setNotes((prev) => prev!.filter((n) => n.id !== note.id))}
+            />
+          ))}
+        </ol>
+      )}
+    </section>
+  )
+}
+
+function NoteItem({ note, onSaved, onDeleted }: { note: Note; onSaved: (note: Note) => void; onDeleted: () => void }) {
+  const [editing, setEditing] = useState(false)
+  const [text, setText] = useState(note.body)
+  const [error, setError] = useState<string | null>(null)
+  const errorId = `note-${note.id}-error`
+
+  async function save(event: FormEvent) {
+    event.preventDefault()
+    setError(null)
+    try {
+      onSaved(await api<Note>('PATCH', `/notes/${note.id}`, { body: text }))
+      setEditing(false)
+    } catch (err) {
+      setError(errorMessage(err))
+    }
+  }
+
+  async function remove() {
+    setError(null)
+    try {
+      await api('DELETE', `/notes/${note.id}`)
+      onDeleted()
+    } catch (err) {
+      setError(errorMessage(err))
+    }
+  }
+
+  return (
+    <li className="border-t border-slate-200 py-3">
+      <p className="text-xs text-slate-500">
+        <time dateTime={note.created_at}>{new Date(note.created_at).toLocaleString()}</time>
+        {note.updated_at !== note.created_at && ' · edited'}
+      </p>
+      {editing ? (
+        <form onSubmit={save} className="mt-1 space-y-2">
+          <label className="block">
+            <span className="sr-only">Edit entry</span>
+            <textarea
+              className={inputClass}
+              rows={3}
+              maxLength={MAX_NOTE}
+              value={text}
+              onChange={(e) => setText(e.target.value)}
+              required
+              aria-describedby={error ? errorId : undefined}
+            />
+          </label>
+          <div className="flex gap-2">
+            <button type="submit" className={primaryButton}>
+              Save
+            </button>
+            <button
+              type="button"
+              className={secondaryButton}
+              onClick={() => {
+                setEditing(false)
+                setText(note.body)
+              }}
+            >
+              Cancel
+            </button>
+          </div>
+        </form>
+      ) : (
+        <>
+          <p className="mt-1 whitespace-pre-wrap">{note.body}</p>
+          <div className="mt-2 flex gap-2">
+            <button type="button" className={secondaryButton} onClick={() => setEditing(true)}>
+              Edit entry
+            </button>
+            <button type="button" className={dangerButton} onClick={() => void remove()}>
+              Delete entry
+            </button>
+          </div>
+        </>
+      )}
+      {error && (
+        <p id={errorId} role="alert" className="mt-2 text-sm text-red-700">
+          {error}
+        </p>
+      )}
+    </li>
+  )
+}