diff --git a/frontend/src/auth/RegisterPage.test.tsx b/frontend/src/auth/RegisterPage.test.tsx
new file mode 100644
index 0000000..7ada828
--- /dev/null
+++ b/frontend/src/auth/RegisterPage.test.tsx
@@ -0,0 +1,172 @@
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import { delay, http, HttpResponse } from 'msw'
+import { MemoryRouter, Route, Routes } from 'react-router'
+import { describe, expect, it } from 'vitest'
+import { server } from '../test/server'
+import { AuthProvider } from './AuthProvider'
+import { RequireGuest } from './guards'
+import RegisterPage from './RegisterPage'
+
+/**
+ * Route tree mirroring the real app skeleton: a guest-only /register rendering
+ * the real RegisterPage, and a /login route showing a marker so we can assert
+ * the post-register navigation actually lands there. Unlike login, a
+ * successful register does NOT flip auth state — it must explicitly navigate.
+ */
+function AppWithRegister() {
+  return (
+    <AuthProvider>
+      <Routes>
+        <Route element={<RequireGuest />}>
+          <Route path="/register" element={<RegisterPage />} />
+          <Route path="/login" element={<div>LOGIN</div>} />
+        </Route>
+      </Routes>
+    </AuthProvider>
+  )
+}
+
+describe('RegisterPage', () => {
+  it('registers with valid input and redirects to the login screen', async () => {
+    let registerBody: unknown
+    server.use(
+      http.get('http://localhost/api/me', () =>
+        HttpResponse.json({ message: 'unauthorized' }, { status: 401 }),
+      ),
+      http.post('http://localhost/api/register', async ({ request }) => {
+        registerBody = await request.json()
+        return HttpResponse.json(
+          { id: 'u1', email: 'new@example.com' },
+          { status: 201 },
+        )
+      }),
+    )
+
+    const user = userEvent.setup()
+
+    render(
+      <MemoryRouter initialEntries={['/register']}>
+        <AppWithRegister />
+      </MemoryRouter>,
+    )
+
+    await user.type(await screen.findByLabelText(/email/i), 'new@example.com')
+    await user.type(screen.getByLabelText(/password/i), 'correct-horse-battery')
+    await user.click(screen.getByRole('button', { name: /register/i }))
+
+    expect(await screen.findByText('LOGIN')).toBeInTheDocument()
+    expect(screen.queryByLabelText(/email/i)).not.toBeInTheDocument()
+
+    // The register endpoint takes email/password — NOT username (login's quirk).
+    expect(registerBody).toEqual({
+      email: 'new@example.com',
+      password: 'correct-horse-battery',
+    })
+  })
+
+  it('renders server-side field errors from a 422', async () => {
+    server.use(
+      http.get('http://localhost/api/me', () =>
+        HttpResponse.json({ message: 'unauthorized' }, { status: 401 }),
+      ),
+      http.post('http://localhost/api/register', () =>
+        HttpResponse.json(
+          {
+            errors: {
+              email: ['This email is already registered.'],
+              password: ['Too short.'],
+            },
+          },
+          { status: 422 },
+        ),
+      ),
+    )
+
+    const user = userEvent.setup()
+
+    render(
+      <MemoryRouter initialEntries={['/register']}>
+        <AppWithRegister />
+      </MemoryRouter>,
+    )
+
+    await user.type(await screen.findByLabelText(/email/i), 'taken@example.com')
+    await user.type(screen.getByLabelText(/password/i), 'short')
+    await user.click(screen.getByRole('button', { name: /register/i }))
+
+    expect(
+      await screen.findByText(/this email is already registered/i),
+    ).toBeInTheDocument()
+    expect(screen.getByText(/too short/i)).toBeInTheDocument()
+
+    // Still on /register — no redirect happened.
+    expect(screen.getByLabelText(/email/i)).toBeInTheDocument()
+    expect(screen.queryByText('LOGIN')).not.toBeInTheDocument()
+  })
+
+  it('shows a duplicate-email error from a 422', async () => {
+    server.use(
+      http.get('http://localhost/api/me', () =>
+        HttpResponse.json({ message: 'unauthorized' }, { status: 401 }),
+      ),
+      http.post('http://localhost/api/register', () =>
+        HttpResponse.json(
+          { errors: { email: ['This email is already registered.'] } },
+          { status: 422 },
+        ),
+      ),
+    )
+
+    const user = userEvent.setup()
+
+    render(
+      <MemoryRouter initialEntries={['/register']}>
+        <AppWithRegister />
+      </MemoryRouter>,
+    )
+
+    await user.type(await screen.findByLabelText(/email/i), 'taken@example.com')
+    await user.type(screen.getByLabelText(/password/i), 'correct-horse-battery')
+    await user.click(screen.getByRole('button', { name: /register/i }))
+
+    expect(
+      await screen.findByText(/this email is already registered/i),
+    ).toBeInTheDocument()
+    expect(screen.getByLabelText(/email/i)).toBeInTheDocument()
+    expect(screen.queryByText('LOGIN')).not.toBeInTheDocument()
+  })
+
+  it('disables the submit button while the request is in flight', async () => {
+    server.use(
+      http.get('http://localhost/api/me', () =>
+        HttpResponse.json({ message: 'unauthorized' }, { status: 401 }),
+      ),
+      http.post('http://localhost/api/register', async () => {
+        await delay(50)
+        return HttpResponse.json(
+          { id: 'u1', email: 'new@example.com' },
+          { status: 201 },
+        )
+      }),
+    )
+
+    const user = userEvent.setup()
+
+    render(
+      <MemoryRouter initialEntries={['/register']}>
+        <AppWithRegister />
+      </MemoryRouter>,
+    )
+
+    await user.type(await screen.findByLabelText(/email/i), 'new@example.com')
+    await user.type(screen.getByLabelText(/password/i), 'correct-horse-battery')
+
+    const submitButton = screen.getByRole('button', { name: /register/i })
+    await user.click(submitButton)
+
+    expect(submitButton).toBeDisabled()
+
+    expect(await screen.findByText('LOGIN')).toBeInTheDocument()
+  })
+})
diff --git a/frontend/src/auth/RegisterPage.tsx b/frontend/src/auth/RegisterPage.tsx
new file mode 100644
index 0000000..60749e5
--- /dev/null
+++ b/frontend/src/auth/RegisterPage.tsx
@@ -0,0 +1,93 @@
+import { useState, type FormEvent } from 'react'
+import { useNavigate } from 'react-router'
+import AppLayout from '../components/layout/AppLayout'
+import Button from '../components/ui/Button'
+import FieldError from '../components/ui/FieldError'
+import Input from '../components/ui/Input'
+import Panel from '../components/ui/Panel'
+import { api } from '../lib/api'
+import { parseFieldErrors, type FieldErrors } from '../lib/fieldErrors'
+
+export default function RegisterPage() {
+  const navigate = useNavigate()
+  const [email, setEmail] = useState('')
+  const [password, setPassword] = useState('')
+  const [fieldErrors, setFieldErrors] = useState<FieldErrors>({})
+  const [formError, setFormError] = useState<string | null>(null)
+  const [pending, setPending] = useState(false)
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault()
+    setFieldErrors({})
+    setFormError(null)
+    setPending(true)
+
+    try {
+      await api.postJson('/register', { email, password })
+      // Register does not establish a session — send the user to sign in.
+      navigate('/login')
+    } catch (err: unknown) {
+      const errors = parseFieldErrors(err)
+      if (errors !== null) {
+        setFieldErrors(errors)
+      } else {
+        setFormError('Registration failed. Please try again.')
+      }
+    } finally {
+      setPending(false)
+    }
+  }
+
+  const emailErrors = fieldErrors.email
+  const passwordErrors = fieldErrors.password
+
+  return (
+    <AppLayout>
+      <Panel className="mx-auto max-w-sm space-y-4">
+        <h2 className="text-primary font-bold uppercase tracking-wider">
+          Register
+        </h2>
+
+        <form className="space-y-4" onSubmit={handleSubmit}>
+          <div className="space-y-1">
+            <Input
+              label="Email"
+              type="email"
+              autoComplete="email"
+              required
+              value={email}
+              onChange={(e) => setEmail(e.target.value)}
+              aria-invalid={emailErrors !== undefined}
+              aria-describedby={emailErrors ? 'email-errors' : undefined}
+            />
+            <FieldError id="email-errors" messages={emailErrors} />
+          </div>
+
+          <div className="space-y-1">
+            <Input
+              label="Password"
+              type="password"
+              autoComplete="new-password"
+              required
+              value={password}
+              onChange={(e) => setPassword(e.target.value)}
+              aria-invalid={passwordErrors !== undefined}
+              aria-describedby={passwordErrors ? 'password-errors' : undefined}
+            />
+            <FieldError id="password-errors" messages={passwordErrors} />
+          </div>
+
+          {formError !== null && (
+            <p role="alert" className="text-destructive font-mono text-sm">
+              {formError}
+            </p>
+          )}
+
+          <Button type="submit" glow disabled={pending} className="w-full">
+            {pending ? 'Registering…' : 'Register'}
+          </Button>
+        </form>
+      </Panel>
+    </AppLayout>
+  )
+}
diff --git a/frontend/src/auth/RegisterPlaceholder.tsx b/frontend/src/auth/RegisterPlaceholder.tsx
deleted file mode 100644
index f11a744..0000000
--- a/frontend/src/auth/RegisterPlaceholder.tsx
+++ /dev/null
@@ -1,4 +0,0 @@
-// Placeholder replaced by the real register screen in #52 Story 5.
-export default function RegisterPlaceholder() {
-  return <div>REGISTER</div>
-}
diff --git a/frontend/src/components/ui/FieldError.tsx b/frontend/src/components/ui/FieldError.tsx
new file mode 100644
index 0000000..410369b
--- /dev/null
+++ b/frontend/src/components/ui/FieldError.tsx
@@ -0,0 +1,26 @@
+interface FieldErrorProps {
+  /** Used as the element id so an input can reference it via aria-describedby. */
+  id?: string
+  messages?: string[]
+}
+
+/**
+ * Renders a form field's validation messages (from a 422 field-error map).
+ * Renders nothing when there are no messages. Each message is a live-region
+ * alert so screen readers announce it when it appears.
+ */
+export default function FieldError({ id, messages }: FieldErrorProps) {
+  if (messages === undefined || messages.length === 0) {
+    return null
+  }
+
+  return (
+    <ul id={id} className="text-destructive font-mono text-sm">
+      {messages.map((message, index) => (
+        <li key={`${message}-${index}`} role="alert">
+          {message}
+        </li>
+      ))}
+    </ul>
+  )
+}
diff --git a/frontend/src/lib/fieldErrors.test.ts b/frontend/src/lib/fieldErrors.test.ts
new file mode 100644
index 0000000..a9b1a2e
--- /dev/null
+++ b/frontend/src/lib/fieldErrors.test.ts
@@ -0,0 +1,46 @@
+import { describe, expect, it } from 'vitest'
+import { ApiError } from './api'
+import { parseFieldErrors } from './fieldErrors'
+
+function error422(body: unknown): ApiError {
+  return new ApiError(422, JSON.stringify(body))
+}
+
+describe('parseFieldErrors', () => {
+  it('extracts a well-formed field-error map from a 422', () => {
+    const result = parseFieldErrors(
+      error422({ errors: { email: ['Already taken.'], password: ['Short.'] } }),
+    )
+
+    expect(result).toEqual({
+      email: ['Already taken.'],
+      password: ['Short.'],
+    })
+  })
+
+  it('returns null for a non-ApiError', () => {
+    expect(parseFieldErrors(new Error('boom'))).toBeNull()
+  })
+
+  it('returns null for a non-422 ApiError', () => {
+    expect(parseFieldErrors(new ApiError(500, 'server error'))).toBeNull()
+  })
+
+  it('returns null when the body is not JSON', () => {
+    expect(parseFieldErrors(new ApiError(422, '<html>nope</html>'))).toBeNull()
+  })
+
+  it('returns null when the body has no errors key', () => {
+    expect(parseFieldErrors(error422({ message: 'bad' }))).toBeNull()
+  })
+
+  it('returns null when a field value is a bare string, not an array', () => {
+    expect(
+      parseFieldErrors(error422({ errors: { email: 'taken' } })),
+    ).toBeNull()
+  })
+
+  it('returns null when a field value is an array of non-strings', () => {
+    expect(parseFieldErrors(error422({ errors: { email: [42] } }))).toBeNull()
+  })
+})
diff --git a/frontend/src/lib/fieldErrors.ts b/frontend/src/lib/fieldErrors.ts
new file mode 100644
index 0000000..2e573fd
--- /dev/null
+++ b/frontend/src/lib/fieldErrors.ts
@@ -0,0 +1,45 @@
+import { ApiError } from './api'
+
+/** Per-field validation messages: a 422 body's `{ errors: { field: [msg] } }`. */
+export type FieldErrors = Record<string, string[]>
+
+function isStringArray(value: unknown): value is string[] {
+  return Array.isArray(value) && value.every((item) => typeof item === 'string')
+}
+
+/**
+ * Extract the `{ errors: { field: [...] } }` map from a 422 ApiError body.
+ * Returns null for anything that isn't a well-formed 422 field-error response
+ * (wrong status, non-ApiError, non-JSON body, or a malformed errors shape) so
+ * the caller can fall back to a generic error message.
+ */
+export function parseFieldErrors(error: unknown): FieldErrors | null {
+  if (!(error instanceof ApiError) || error.status !== 422) {
+    return null
+  }
+
+  let parsed: unknown
+  try {
+    parsed = JSON.parse(error.body)
+  } catch {
+    return null
+  }
+
+  if (
+    typeof parsed !== 'object' ||
+    parsed === null ||
+    !('errors' in parsed) ||
+    typeof parsed.errors !== 'object' ||
+    parsed.errors === null
+  ) {
+    return null
+  }
+
+  // Only accept the contract shape: every field maps to an array of strings.
+  const entries = Object.entries(parsed.errors as Record<string, unknown>)
+  if (!entries.every(([, messages]) => isStringArray(messages))) {
+    return null
+  }
+
+  return parsed.errors as FieldErrors
+}
diff --git a/frontend/src/router.tsx b/frontend/src/router.tsx
index 13005d5..d33ac3b 100644
--- a/frontend/src/router.tsx
+++ b/frontend/src/router.tsx
@@ -1,6 +1,6 @@
 import { createBrowserRouter, Navigate, type RouteObject } from 'react-router'
 import LoginPage from './auth/LoginPage'
-import RegisterPlaceholder from './auth/RegisterPlaceholder'
+import RegisterPage from './auth/RegisterPage'
 import { RequireAuth, RequireGuest } from './auth/guards'
 import ScenariosPage from './pages/ScenariosPage'
 
@@ -18,7 +18,7 @@ export const routes: RouteObject[] = [
     element: <RequireGuest />,
     children: [
       { path: '/login', element: <LoginPage /> },
-      { path: '/register', element: <RegisterPlaceholder /> },
+      { path: '/register', element: <RegisterPage /> },
     ],
   },
   {