diff --git a/src/__tests__/login.test.ts b/src/__tests__/login.test.ts
new file mode 100644
index 0000000..6dd68fc
--- /dev/null
+++ b/src/__tests__/login.test.ts
@@ -0,0 +1,105 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { Command } from 'commander'
+
+// Mock the auth module
+vi.mock('../lib/auth.js', () => ({
+  saveApiToken: vi.fn(),
+}))
+
+// Mock the config module
+vi.mock('../lib/config.js', () => ({
+  getConfigPath: vi.fn(() => '/home/user/.config/twist-cli/config.json'),
+}))
+
+// Mock chalk to avoid colors in tests
+vi.mock('chalk', () => ({
+  default: {
+    green: vi.fn((text) => text),
+    dim: vi.fn((text) => text),
+  },
+}))
+
+import { saveApiToken } from '../lib/auth.js'
+import { getConfigPath } from '../lib/config.js'
+import { registerLoginCommand } from '../commands/login.js'
+
+const mockSaveApiToken = vi.mocked(saveApiToken)
+const mockGetConfigPath = vi.mocked(getConfigPath)
+
+function createProgram() {
+  const program = new Command()
+  program.exitOverride()
+  registerLoginCommand(program)
+  return program
+}
+
+describe('login command', () => {
+  let consoleSpy: ReturnType<typeof vi.spyOn>
+
+  beforeEach(() => {
+    vi.clearAllMocks()
+
+    // Mock console.log to capture output
+    consoleSpy = vi.spyOn(console, 'log').mockImplementation(() => {})
+  })
+
+  afterEach(() => {
+    consoleSpy.mockRestore()
+  })
+
+  describe('token subcommand', () => {
+    it('successfully saves a token', async () => {
+      const program = createProgram()
+      const token = 'some_token_123456789'
+
+      // Mock successful token save
+      mockSaveApiToken.mockResolvedValue(undefined)
+
+      await program.parseAsync(['node', 'tw', 'login', 'token', token])
+
+      // Verify token was saved
+      expect(mockSaveApiToken).toHaveBeenCalledWith(token)
+
+      // Verify success message
+      expect(consoleSpy).toHaveBeenCalledWith('✓', 'API token saved successfully!')
+      expect(consoleSpy).toHaveBeenCalledWith(
+        'Token saved to /home/user/.config/twist-cli/config.json',
+      )
+    })
+
+    it('handles saveApiToken errors', async () => {
+      const program = createProgram()
+      const token = 'some_token_123456789'
+
+      // Mock save failure
+      mockSaveApiToken.mockRejectedValue(new Error('Permission denied'))
+
+      await expect(program.parseAsync(['node', 'tw', 'login', 'token', token])).rejects.toThrow(
+        'Permission denied',
+      )
+
+      expect(mockSaveApiToken).toHaveBeenCalledWith(token)
+    })
+
+    it('trims whitespace from token', async () => {
+      const program = createProgram()
+      const tokenWithWhitespace = '  some_token_123456789  '
+      const expectedToken = 'some_token_123456789'
+
+      mockSaveApiToken.mockResolvedValue(undefined)
+
+      await program.parseAsync(['node', 'tw', 'login', 'token', tokenWithWhitespace])
+
+      expect(mockSaveApiToken).toHaveBeenCalledWith(expectedToken)
+    })
+
+    it('shows help when no arguments provided', async () => {
+      const program = createProgram()
+
+      // This should show help for the login command
+      await expect(program.parseAsync(['node', 'tw', 'login'])).rejects.toThrow() // Commander throws when required argument is missing
+
+      expect(mockSaveApiToken).not.toHaveBeenCalled()
+    })
+  })
+})
diff --git a/src/commands/login.ts b/src/commands/login.ts
new file mode 100644
index 0000000..db26389
--- /dev/null
+++ b/src/commands/login.ts
@@ -0,0 +1,22 @@
+import { Command } from 'commander'
+import { saveApiToken } from '../lib/auth.js'
+import { getConfigPath } from '../lib/config.js'
+import chalk from 'chalk'
+
+async function loginWithToken(token: string): Promise<void> {
+  try {
+    // Save token to config
+    await saveApiToken(token.trim())
+
+    console.log(chalk.green('✓'), 'API token saved successfully!')
+    console.log(chalk.dim(`Token saved to ${getConfigPath()}`))
+  } catch (error: any) {
+    throw error
+  }
+}
+
+export function registerLoginCommand(program: Command): void {
+  const login = program.command('login').description('Authenticate with Twist')
+
+  login.command('token <token>').description('Save API token to config file').action(loginWithToken)
+}
diff --git a/src/index.ts b/src/index.ts
index d8dcdfe..f668bf3 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -9,6 +9,7 @@ import { registerThreadCommand } from './commands/thread.js'
 import { registerMsgCommand } from './commands/msg.js'
 import { registerSearchCommand } from './commands/search.js'
 import { registerReactCommand } from './commands/react.js'
+import { registerLoginCommand } from './commands/login.js'
 
 program
   .name('tw')
@@ -30,5 +31,6 @@ registerThreadCommand(program)
 registerMsgCommand(program)
 registerSearchCommand(program)
 registerReactCommand(program)
+registerLoginCommand(program)
 
 program.parse()
diff --git a/src/lib/auth.ts b/src/lib/auth.ts
index 00ecdbe..7e08260 100644
--- a/src/lib/auth.ts
+++ b/src/lib/auth.ts
@@ -1,4 +1,4 @@
-import { getConfig, getConfigPath } from './config.js'
+import { getConfig, getConfigPath, updateConfig } from './config.js'
 
 export async function getApiToken(): Promise<string> {
   const envToken = process.env.TWIST_API_TOKEN
@@ -15,3 +15,13 @@ export async function getApiToken(): Promise<string> {
     `No API token found. Set TWIST_API_TOKEN environment variable or add "token" to ${getConfigPath()}`,
   )
 }
+
+export async function saveApiToken(token: string): Promise<void> {
+  // Validate token (non-empty, reasonable length)
+  if (!token || token.trim().length < 10) {
+    throw new Error('Invalid token: Token must be at least 10 characters')
+  }
+
+  // Update config with new token using the existing config system
+  await updateConfig({ token: token.trim() })
+}