diff --git a/__tests__/api.integration.test.ts b/__tests__/api.integration.test.ts
index 1a3727f..ad7a9cc 100644
--- a/__tests__/api.integration.test.ts
+++ b/__tests__/api.integration.test.ts
@@ -38,6 +38,11 @@ const mockPrisma = {
     create: jest.fn(),
     createMany: jest.fn(),
   },
+  noteVersion: {
+    create: jest.fn(),
+    findMany: jest.fn(),
+    findUnique: jest.fn(),
+  },
   $transaction: jest.fn((callback) => callback(mockPrisma)),
 }
 
diff --git a/__tests__/versions.test.ts b/__tests__/versions.test.ts
new file mode 100644
index 0000000..f6a0482
--- /dev/null
+++ b/__tests__/versions.test.ts
@@ -0,0 +1,167 @@
+import { createVersion, getVersions, getVersion, restoreVersion } from '@/lib/versions'
+
+jest.mock('@/lib/prisma', () => ({
+  prisma: {
+    note: { findUnique: jest.fn(), update: jest.fn() },
+    noteVersion: { create: jest.fn(), findMany: jest.fn(), findUnique: jest.fn() },
+  },
+}))
+
+import { prisma } from '@/lib/prisma'
+import { NotFoundError } from '@/lib/errors'
+
+describe('versions.ts', () => {
+  beforeEach(() => {
+    jest.clearAllMocks()
+  })
+
+  describe('createVersion', () => {
+    it('creates a version with correct noteId, title, content', async () => {
+      const mockNote = { id: 'note-1', title: 'Test Title', content: 'Test Content' }
+      const mockVersion = { id: 'version-1', noteId: 'note-1', title: 'Test Title', content: 'Test Content', createdAt: new Date() }
+
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue(mockNote)
+      ;(prisma.noteVersion.create as jest.Mock).mockResolvedValue(mockVersion)
+
+      const result = await createVersion('note-1')
+
+      expect(result).toEqual(mockVersion)
+      expect(prisma.note.findUnique).toHaveBeenCalledWith({
+        where: { id: 'note-1' },
+        select: { id: true, title: true, content: true },
+      })
+      expect(prisma.noteVersion.create).toHaveBeenCalledWith({
+        data: {
+          noteId: 'note-1',
+          title: 'Test Title',
+          content: 'Test Content',
+        },
+      })
+    })
+
+    it('throws NotFoundError if note does not exist', async () => {
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue(null)
+
+      await expect(createVersion('note-1')).rejects.toThrow(NotFoundError)
+    })
+  })
+
+  describe('getVersions', () => {
+    it('returns all versions for a note ordered by createdAt desc', async () => {
+      const mockNote = { id: 'note-1' }
+      const mockVersions = [
+        { id: 'version-2', noteId: 'note-1', title: 'Title 2', content: 'Content 2', createdAt: new Date('2024-01-02') },
+        { id: 'version-1', noteId: 'note-1', title: 'Title 1', content: 'Content 1', createdAt: new Date('2024-01-01') },
+      ]
+
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue(mockNote)
+      ;(prisma.noteVersion.findMany as jest.Mock).mockResolvedValue(mockVersions)
+
+      const result = await getVersions('note-1')
+
+      expect(result).toEqual(mockVersions)
+      expect(prisma.note.findUnique).toHaveBeenCalledWith({ where: { id: 'note-1' } })
+      expect(prisma.noteVersion.findMany).toHaveBeenCalledWith({
+        where: { noteId: 'note-1' },
+        orderBy: { createdAt: 'desc' },
+        select: {
+          id: true,
+          noteId: true,
+          title: true,
+          content: true,
+          createdAt: true,
+        },
+      })
+    })
+
+    it('throws NotFoundError if note does not exist', async () => {
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue(null)
+
+      await expect(getVersions('note-1')).rejects.toThrow(NotFoundError)
+    })
+  })
+
+  describe('getVersion', () => {
+    it('returns version by ID', async () => {
+      const mockVersion = { id: 'version-1', noteId: 'note-1', title: 'Title', content: 'Content', createdAt: new Date() }
+
+      ;(prisma.noteVersion.findUnique as jest.Mock).mockResolvedValue(mockVersion)
+
+      const result = await getVersion('version-1')
+
+      expect(result).toEqual(mockVersion)
+      expect(prisma.noteVersion.findUnique).toHaveBeenCalledWith({ where: { id: 'version-1' } })
+    })
+
+    it('throws NotFoundError if version does not exist', async () => {
+      ;(prisma.noteVersion.findUnique as jest.Mock).mockResolvedValue(null)
+
+      await expect(getVersion('version-1')).rejects.toThrow(NotFoundError)
+    })
+  })
+
+  describe('restoreVersion', () => {
+    it('updates note title and content from version', async () => {
+      const mockNote = { id: 'note-1', title: 'Old Title', content: 'Old Content' }
+      const mockVersion = { id: 'version-1', noteId: 'note-1', title: 'Old Title', content: 'Old Content', createdAt: new Date() }
+      const updatedNote = { id: 'note-1', title: 'Old Title', content: 'Old Content', updatedAt: new Date() }
+
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue(mockNote)
+      ;(prisma.noteVersion.findUnique as jest.Mock).mockResolvedValue(mockVersion)
+      ;(prisma.note.update as jest.Mock).mockResolvedValue(updatedNote)
+
+      const result = await restoreVersion('note-1', 'version-1')
+
+      expect(result).toEqual(updatedNote)
+      expect(prisma.note.update).toHaveBeenCalledWith({
+        where: { id: 'note-1' },
+        data: {
+          title: 'Old Title',
+          content: 'Old Content',
+          updatedAt: expect.any(Date),
+        },
+        select: {
+          id: true,
+          title: true,
+          content: true,
+          updatedAt: true,
+        },
+      })
+    })
+
+    it('updates note updatedAt timestamp', async () => {
+      const mockNote = { id: 'note-1', title: 'Title', content: 'Content' }
+      const mockVersion = { id: 'version-1', noteId: 'note-1', title: 'Title', content: 'Content', createdAt: new Date() }
+      const beforeUpdate = new Date('2024-01-01')
+      const afterUpdate = new Date('2024-01-02')
+
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue(mockNote)
+      ;(prisma.noteVersion.findUnique as jest.Mock).mockResolvedValue(mockVersion)
+      ;(prisma.note.update as jest.Mock).mockResolvedValue({ id: 'note-1', title: 'Title', content: 'Content', updatedAt: afterUpdate })
+
+      const result = await restoreVersion('note-1', 'version-1')
+
+      expect(result.updatedAt).toEqual(afterUpdate)
+    })
+
+    it('throws NotFoundError if note does not exist', async () => {
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue(null)
+
+      await expect(restoreVersion('note-1', 'version-1')).rejects.toThrow(NotFoundError)
+    })
+
+    it('throws NotFoundError if version does not exist', async () => {
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue({ id: 'note-1' })
+      ;(prisma.noteVersion.findUnique as jest.Mock).mockResolvedValue(null)
+
+      await expect(restoreVersion('note-1', 'version-1')).rejects.toThrow(NotFoundError)
+    })
+
+    it('throws NotFoundError if version does not belong to note', async () => {
+      ;(prisma.note.findUnique as jest.Mock).mockResolvedValue({ id: 'note-1' })
+      ;(prisma.noteVersion.findUnique as jest.Mock).mockResolvedValue({ id: 'version-1', noteId: 'note-2' })
+
+      await expect(restoreVersion('note-1', 'version-1')).rejects.toThrow(NotFoundError)
+    })
+  })
+})