diff --git a/src/design-system/composites/LoginForm/LoginDialog.test.tsx b/src/design-system/composites/LoginForm/LoginDialog.test.tsx
new file mode 100644
index 0000000..6e486d0
--- /dev/null
+++ b/src/design-system/composites/LoginForm/LoginDialog.test.tsx
@@ -0,0 +1,54 @@
+import { describe, it, expect, vi } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import { LoginDialog } from './LoginDialog'
+
+const defaultProps = {
+  open: true,
+  onClose: vi.fn(),
+  onSubmit: vi.fn(),
+}
+
+describe('LoginDialog', () => {
+  it('renders Modal with LoginForm when open', () => {
+    render(<LoginDialog {...defaultProps} />)
+    expect(screen.getByRole('dialog')).toBeInTheDocument()
+    expect(screen.getByRole('heading', { name: 'Sign in' })).toBeInTheDocument()
+    expect(screen.getByLabelText(/email/i)).toBeInTheDocument()
+  })
+
+  it('does not render when closed', () => {
+    render(<LoginDialog {...defaultProps} open={false} />)
+    expect(screen.queryByRole('dialog')).not.toBeInTheDocument()
+  })
+
+  it('calls onClose on Esc', async () => {
+    const onClose = vi.fn()
+    const user = userEvent.setup()
+    render(<LoginDialog {...defaultProps} onClose={onClose} />)
+    await user.keyboard('{Escape}')
+    expect(onClose).toHaveBeenCalled()
+  })
+
+  it('calls onClose on backdrop click', async () => {
+    const onClose = vi.fn()
+    const user = userEvent.setup()
+    render(<LoginDialog {...defaultProps} onClose={onClose} />)
+    await user.click(screen.getByTestId('modal-backdrop'))
+    expect(onClose).toHaveBeenCalled()
+  })
+
+  it('passes LoginForm props through', () => {
+    render(
+      <LoginDialog
+        {...defaultProps}
+        title="Welcome"
+        socialProviders={[{ label: 'Continue with Google', onClick: vi.fn() }]}
+        error="Bad credentials"
+      />,
+    )
+    expect(screen.getByText('Welcome')).toBeInTheDocument()
+    expect(screen.getByText('Continue with Google')).toBeInTheDocument()
+    expect(screen.getByText('Bad credentials')).toBeInTheDocument()
+  })
+})
diff --git a/src/design-system/composites/LoginForm/LoginDialog.tsx b/src/design-system/composites/LoginForm/LoginDialog.tsx
new file mode 100644
index 0000000..cffd740
--- /dev/null
+++ b/src/design-system/composites/LoginForm/LoginDialog.tsx
@@ -0,0 +1,15 @@
+import { Modal } from '../Modal/Modal'
+import { LoginForm, type LoginFormProps } from './LoginForm'
+
+export interface LoginDialogProps extends LoginFormProps {
+  open: boolean
+  onClose: () => void
+}
+
+export function LoginDialog({ open, onClose, className, ...formProps }: LoginDialogProps) {
+  return (
+    <Modal open={open} onClose={onClose} size="sm" className={className}>
+      <LoginForm {...formProps} />
+    </Modal>
+  )
+}
diff --git a/src/design-system/composites/LoginForm/LoginForm.module.css b/src/design-system/composites/LoginForm/LoginForm.module.css
new file mode 100644
index 0000000..5c61959
--- /dev/null
+++ b/src/design-system/composites/LoginForm/LoginForm.module.css
@@ -0,0 +1,111 @@
+.loginForm {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  font-family: var(--font-body);
+  width: 100%;
+}
+
+.logo {
+  margin-bottom: 8px;
+}
+
+.title {
+  font-size: 16px;
+  font-weight: 600;
+  color: var(--text-primary);
+  margin: 0 0 20px;
+}
+
+.error {
+  width: 100%;
+  margin-bottom: 16px;
+}
+
+.socialSection {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  width: 100%;
+  margin-bottom: 20px;
+}
+
+.socialButton {
+  width: 100%;
+  justify-content: center;
+}
+
+.divider {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  width: 100%;
+  margin-bottom: 20px;
+}
+
+.dividerLine {
+  flex: 1;
+  height: 1px;
+  background: var(--border);
+}
+
+.dividerText {
+  color: var(--text-muted);
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+  font-weight: 500;
+}
+
+.fields {
+  display: flex;
+  flex-direction: column;
+  gap: 14px;
+  width: 100%;
+}
+
+.rememberRow {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+}
+
+.forgotLink {
+  font-size: 11px;
+  color: var(--amber);
+  font-weight: 500;
+  background: none;
+  border: none;
+  cursor: pointer;
+  padding: 0;
+  font-family: var(--font-body);
+}
+
+.forgotLink:hover {
+  text-decoration: underline;
+}
+
+.submitButton {
+  width: 100%;
+}
+
+.signUpText {
+  text-align: center;
+  font-size: 12px;
+  color: var(--text-secondary);
+}
+
+.signUpLink {
+  color: var(--amber);
+  font-weight: 500;
+  background: none;
+  border: none;
+  cursor: pointer;
+  padding: 0;
+  font-family: var(--font-body);
+  font-size: 12px;
+}
+
+.signUpLink:hover {
+  text-decoration: underline;
+}
diff --git a/src/design-system/composites/LoginForm/LoginForm.test.tsx b/src/design-system/composites/LoginForm/LoginForm.test.tsx
new file mode 100644
index 0000000..a6b1e88
--- /dev/null
+++ b/src/design-system/composites/LoginForm/LoginForm.test.tsx
@@ -0,0 +1,193 @@
+import { describe, it, expect, vi } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import { LoginForm } from './LoginForm'
+
+const socialProviders = [
+  { label: 'Continue with Google', onClick: vi.fn() },
+  { label: 'Continue with GitHub', onClick: vi.fn() },
+]
+
+const allProps = {
+  logo: <div data-testid="logo">Logo</div>,
+  title: 'Welcome back',
+  socialProviders,
+  onSubmit: vi.fn(),
+  onForgotPassword: vi.fn(),
+  onSignUp: vi.fn(),
+}
+
+describe('LoginForm', () => {
+  describe('rendering', () => {
+    it('renders all elements when all props provided', () => {
+      render(<LoginForm {...allProps} />)
+      expect(screen.getByTestId('logo')).toBeInTheDocument()
+      expect(screen.getByText('Welcome back')).toBeInTheDocument()
+      expect(screen.getByText('Continue with Google')).toBeInTheDocument()
+      expect(screen.getByText('Continue with GitHub')).toBeInTheDocument()
+      expect(screen.getByText('or')).toBeInTheDocument()
+      expect(screen.getByLabelText(/email/i)).toBeInTheDocument()
+      expect(screen.getByLabelText(/password/i)).toBeInTheDocument()
+      expect(screen.getByLabelText(/remember me/i)).toBeInTheDocument()
+      expect(screen.getByText(/forgot password/i)).toBeInTheDocument()
+      expect(screen.getByRole('button', { name: 'Sign in' })).toBeInTheDocument()
+      expect(screen.getByText(/sign up/i)).toBeInTheDocument()
+    })
+
+    it('renders default title when title prop omitted', () => {
+      render(<LoginForm onSubmit={vi.fn()} />)
+      expect(screen.getByRole('heading', { name: 'Sign in' })).toBeInTheDocument()
+    })
+
+    it('hides social section when socialProviders is empty', () => {
+      render(<LoginForm onSubmit={vi.fn()} socialProviders={[]} />)
+      expect(screen.queryByText('or')).not.toBeInTheDocument()
+    })
+
+    it('hides social section when socialProviders is omitted', () => {
+      render(<LoginForm onSubmit={vi.fn()} />)
+      expect(screen.queryByText('or')).not.toBeInTheDocument()
+    })
+
+    it('hides forgot password link when onForgotPassword omitted', () => {
+      render(<LoginForm onSubmit={vi.fn()} />)
+      expect(screen.queryByText(/forgot password/i)).not.toBeInTheDocument()
+    })
+
+    it('hides sign up link when onSignUp omitted', () => {
+      render(<LoginForm onSubmit={vi.fn()} />)
+      expect(screen.queryByText(/sign up/i)).not.toBeInTheDocument()
+    })
+
+    it('hides credentials section when onSubmit omitted (social only)', () => {
+      render(<LoginForm socialProviders={socialProviders} />)
+      expect(screen.queryByLabelText(/email/i)).not.toBeInTheDocument()
+      expect(screen.queryByLabelText(/password/i)).not.toBeInTheDocument()
+      expect(screen.queryByRole('button', { name: 'Sign in' })).not.toBeInTheDocument()
+      expect(screen.queryByText('or')).not.toBeInTheDocument()
+      // Social buttons should still render
+      expect(screen.getByText('Continue with Google')).toBeInTheDocument()
+    })
+
+    it('shows server error Alert when error prop set', () => {
+      render(<LoginForm onSubmit={vi.fn()} error="Invalid credentials" />)
+      expect(screen.getByText('Invalid credentials')).toBeInTheDocument()
+    })
+  })
+
+  describe('validation', () => {
+    it('validates required email', async () => {
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={vi.fn()} />)
+      await user.click(screen.getByRole('button', { name: 'Sign in' }))
+      expect(screen.getByText('Email is required')).toBeInTheDocument()
+    })
+
+    it('validates email format', async () => {
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={vi.fn()} />)
+      await user.type(screen.getByLabelText(/email/i), 'notanemail')
+      await user.type(screen.getByLabelText(/password/i), 'password123')
+      await user.click(screen.getByRole('button', { name: 'Sign in' }))
+      expect(screen.getByText('Please enter a valid email address')).toBeInTheDocument()
+    })
+
+    it('validates required password', async () => {
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={vi.fn()} />)
+      await user.type(screen.getByLabelText(/email/i), 'test@example.com')
+      await user.click(screen.getByRole('button', { name: 'Sign in' }))
+      expect(screen.getByText('Password is required')).toBeInTheDocument()
+    })
+
+    it('validates password minimum length', async () => {
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={vi.fn()} />)
+      await user.type(screen.getByLabelText(/email/i), 'test@example.com')
+      await user.type(screen.getByLabelText(/password/i), 'short')
+      await user.click(screen.getByRole('button', { name: 'Sign in' }))
+      expect(screen.getByText('Password must be at least 8 characters')).toBeInTheDocument()
+    })
+
+    it('clears field errors on typing', async () => {
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={vi.fn()} />)
+      await user.click(screen.getByRole('button', { name: 'Sign in' }))
+      expect(screen.getByText('Email is required')).toBeInTheDocument()
+      await user.type(screen.getByLabelText(/email/i), 't')
+      expect(screen.queryByText('Email is required')).not.toBeInTheDocument()
+    })
+
+    it('calls onSubmit with credentials when valid', async () => {
+      const onSubmit = vi.fn()
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={onSubmit} />)
+      await user.type(screen.getByLabelText(/email/i), 'test@example.com')
+      await user.type(screen.getByLabelText(/password/i), 'password123')
+      await user.click(screen.getByLabelText(/remember me/i))
+      await user.click(screen.getByRole('button', { name: 'Sign in' }))
+      expect(onSubmit).toHaveBeenCalledWith({
+        email: 'test@example.com',
+        password: 'password123',
+        remember: true,
+      })
+    })
+
+    it('does not call onSubmit when validation fails', async () => {
+      const onSubmit = vi.fn()
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={onSubmit} />)
+      await user.click(screen.getByRole('button', { name: 'Sign in' }))
+      expect(onSubmit).not.toHaveBeenCalled()
+    })
+  })
+
+  describe('loading state', () => {
+    it('disables form inputs when loading', () => {
+      render(<LoginForm {...allProps} loading />)
+      expect(screen.getByLabelText(/email/i)).toBeDisabled()
+      expect(screen.getByLabelText(/password/i)).toBeDisabled()
+      expect(screen.getByLabelText(/remember me/i)).toBeDisabled()
+    })
+
+    it('shows spinner on submit button when loading', () => {
+      render(<LoginForm {...allProps} loading />)
+      const submitBtn = screen.getByRole('button', { name: /sign in/i })
+      expect(submitBtn).toBeDisabled()
+      // Button component renders Spinner when loading=true
+      expect(submitBtn.querySelector('[class*="spinner"]')).toBeInTheDocument()
+    })
+
+    it('disables social buttons when loading', () => {
+      render(<LoginForm {...allProps} loading />)
+      expect(screen.getByRole('button', { name: 'Continue with Google' })).toBeDisabled()
+      expect(screen.getByRole('button', { name: 'Continue with GitHub' })).toBeDisabled()
+    })
+  })
+
+  describe('callbacks', () => {
+    it('calls social provider onClick when clicked', async () => {
+      const onClick = vi.fn()
+      const user = userEvent.setup()
+      render(<LoginForm socialProviders={[{ label: 'Continue with Google', onClick }]} onSubmit={vi.fn()} />)
+      await user.click(screen.getByRole('button', { name: 'Continue with Google' }))
+      expect(onClick).toHaveBeenCalledOnce()
+    })
+
+    it('calls onForgotPassword when link clicked', async () => {
+      const onForgotPassword = vi.fn()
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={vi.fn()} onForgotPassword={onForgotPassword} />)
+      await user.click(screen.getByText(/forgot password/i))
+      expect(onForgotPassword).toHaveBeenCalledOnce()
+    })
+
+    it('calls onSignUp when link clicked', async () => {
+      const onSignUp = vi.fn()
+      const user = userEvent.setup()
+      render(<LoginForm onSubmit={vi.fn()} onSignUp={onSignUp} />)
+      await user.click(screen.getByText(/sign up/i))
+      expect(onSignUp).toHaveBeenCalledOnce()
+    })
+  })
+})
diff --git a/src/design-system/composites/LoginForm/LoginForm.tsx b/src/design-system/composites/LoginForm/LoginForm.tsx
new file mode 100644
index 0000000..c4d9ed0
--- /dev/null
+++ b/src/design-system/composites/LoginForm/LoginForm.tsx
@@ -0,0 +1,223 @@
+import { useEffect, useRef, useState, type ReactNode, type FormEvent } from 'react'
+import { Button } from '../../primitives/Button/Button'
+import { Input } from '../../primitives/Input/Input'
+import { Checkbox } from '../../primitives/Checkbox/Checkbox'
+import { FormField } from '../../primitives/FormField/FormField'
+import { Alert } from '../../primitives/Alert/Alert'
+import styles from './LoginForm.module.css'
+
+export interface SocialProvider {
+  label: string
+  icon?: ReactNode
+  onClick: () => void
+}
+
+export interface LoginFormProps {
+  logo?: ReactNode
+  title?: string
+  socialProviders?: SocialProvider[]
+  onSubmit?: (credentials: { email: string; password: string; remember: boolean }) => void
+  onForgotPassword?: () => void
+  onSignUp?: () => void
+  error?: string
+  loading?: boolean
+  className?: string
+}
+
+interface FieldErrors {
+  email?: string
+  password?: string
+}
+
+const EMAIL_REGEX = /^[^\s@]+@[^\s@]+\.[^\s@]+$/
+
+function validate(email: string, password: string): FieldErrors {
+  const errors: FieldErrors = {}
+  if (!email) {
+    errors.email = 'Email is required'
+  } else if (!EMAIL_REGEX.test(email)) {
+    errors.email = 'Please enter a valid email address'
+  }
+  if (!password) {
+    errors.password = 'Password is required'
+  } else if (password.length < 8) {
+    errors.password = 'Password must be at least 8 characters'
+  }
+  return errors
+}
+
+export function LoginForm({
+  logo,
+  title = 'Sign in',
+  socialProviders,
+  onSubmit,
+  onForgotPassword,
+  onSignUp,
+  error,
+  loading = false,
+  className,
+}: LoginFormProps) {
+  const [email, setEmail] = useState('')
+  const [password, setPassword] = useState('')
+  const [remember, setRemember] = useState(false)
+  const [fieldErrors, setFieldErrors] = useState<FieldErrors>({})
+  const [submitted, setSubmitted] = useState(false)
+  const emailRef = useRef<HTMLInputElement>(null)
+
+  // Auto-focus first input on mount
+  useEffect(() => {
+    emailRef.current?.focus()
+  }, [])
+
+  // Reset submitted flag when error prop changes (new server error from re-attempt)
+  useEffect(() => {
+    if (error) setSubmitted(false)
+  }, [error])
+
+  // Server error is shown from prop, hidden after next submit attempt
+  const showServerError = error && !submitted
+
+  const hasSocial = socialProviders && socialProviders.length > 0
+  const hasCredentials = !!onSubmit
+  const showDivider = hasSocial && hasCredentials
+
+  function handleSubmit(e: FormEvent) {
+    e.preventDefault()
+    setSubmitted(true)
+    const errors = validate(email, password)
+    setFieldErrors(errors)
+    if (Object.keys(errors).length === 0) {
+      onSubmit?.({ email, password, remember })
+    }
+  }
+
+  return (
+    <div className={`${styles.loginForm} ${className ?? ''}`}>
+      {logo && <div className={styles.logo}>{logo}</div>}
+      <h2 className={styles.title}>{title}</h2>
+
+      {showServerError && (
+        <div className={styles.error}>
+          <Alert variant="error">{error}</Alert>
+        </div>
+      )}
+
+      {hasSocial && (
+        <div className={styles.socialSection}>
+          {socialProviders.map((provider) => (
+            <Button
+              key={provider.label}
+              variant="secondary"
+              className={styles.socialButton}
+              onClick={provider.onClick}
+              disabled={loading}
+              type="button"
+            >
+              {provider.icon}
+              {provider.label}
+            </Button>
+          ))}
+        </div>
+      )}
+
+      {showDivider && (
+        <div className={styles.divider}>
+          <div className={styles.dividerLine} />
+          <span className={styles.dividerText}>or</span>
+          <div className={styles.dividerLine} />
+        </div>
+      )}
+
+      {hasCredentials && (
+        <form
+          className={styles.fields}
+          onSubmit={handleSubmit}
+          aria-label="Sign in"
+          noValidate
+        >
+          <FormField label="Email" htmlFor="login-email" required error={fieldErrors.email}>
+            <Input
+              ref={emailRef}
+              id="login-email"
+              type="email"
+              placeholder="you@example.com"
+              value={email}
+              onChange={(e) => {
+                setEmail(e.target.value)
+                if (fieldErrors.email) setFieldErrors((prev) => ({ ...prev, email: undefined }))
+              }}
+              disabled={loading}
+            />
+          </FormField>
+
+          <FormField label="Password" htmlFor="login-password" required error={fieldErrors.password}>
+            <Input
+              id="login-password"
+              type="password"
+              placeholder="••••••••"
+              value={password}
+              onChange={(e) => {
+                setPassword(e.target.value)
+                if (fieldErrors.password) setFieldErrors((prev) => ({ ...prev, password: undefined }))
+              }}
+              disabled={loading}
+            />
+          </FormField>
+
+          <div className={styles.rememberRow}>
+            <Checkbox
+              label="Remember me"
+              checked={remember}
+              onChange={(e) => setRemember(e.target.checked)}
+              disabled={loading}
+            />
+            {onForgotPassword && (
+              <button
+                type="button"
+                className={styles.forgotLink}
+                onClick={onForgotPassword}
+              >
+                Forgot password?
+              </button>
+            )}
+          </div>
+
+          <Button
+            variant="primary"
+            type="submit"
+            loading={loading}
+            className={styles.submitButton}
+          >
+            Sign in
+          </Button>
+
+          {onSignUp && (
+            <div className={styles.signUpText}>
+              Don&apos;t have an account?{' '}
+              <button
+                type="button"
+                className={styles.signUpLink}
+                onClick={onSignUp}
+              >
+                Sign up
+              </button>
+            </div>
+          )}
+        </form>
+      )}
+
+      {!hasCredentials && onSignUp && (
+        <div className={styles.signUpText}>
+          Don&apos;t have an account?{' '}
+          <button
+            type="button"
+            className={styles.signUpLink}
+            onClick={onSignUp}
+          >
+            Sign up
+          </button>
+        </div>
+      )}
+    </div>
+  )
+}
diff --git a/src/design-system/composites/index.ts b/src/design-system/composites/index.ts
index f2bb125..4a4ec9b 100644
--- a/src/design-system/composites/index.ts
+++ b/src/design-system/composites/index.ts
@@ -17,6 +17,10 @@ export { GroupCard } from './GroupCard/GroupCard'
 export type { FeedEvent } from './EventFeed/EventFeed'
 export { FilterBar } from './FilterBar/FilterBar'
 export { LineChart } from './LineChart/LineChart'
+export { LoginDialog } from './LoginForm/LoginDialog'
+export type { LoginDialogProps } from './LoginForm/LoginDialog'
+export { LoginForm } from './LoginForm/LoginForm'
+export type { LoginFormProps, SocialProvider } from './LoginForm/LoginForm'
 export { MenuItem } from './MenuItem/MenuItem'
 export { Modal } from './Modal/Modal'
 export { MultiSelect } from './MultiSelect/MultiSelect'