diff --git a/__tests__/types/highlights.test.ts b/__tests__/types/highlights.test.ts
new file mode 100644
index 0000000..8e382cd
--- /dev/null
+++ b/__tests__/types/highlights.test.ts
@@ -0,0 +1,40 @@
+import { BibleHighlight } from '@/types'
+
+describe('BibleHighlight types', () => {
+  it('should create highlight with valid color', () => {
+    const highlight: BibleHighlight = {
+      id: 'test-id',
+      verseId: 'verse-123',
+      color: 'yellow',
+      createdAt: Date.now(),
+      updatedAt: Date.now(),
+      syncStatus: 'synced'
+    }
+    expect(highlight.color).toBe('yellow')
+  })
+
+  it('should reject invalid color', () => {
+    // This test validates TypeScript type checking
+    const highlight: BibleHighlight = {
+      id: 'test-id',
+      verseId: 'verse-123',
+      // @ts-expect-error - 'red' is not a valid color
+      color: 'red',
+      createdAt: Date.now(),
+      updatedAt: Date.now(),
+      syncStatus: 'synced'
+    }
+  })
+
+  it('should validate syncStatus types', () => {
+    const highlight: BibleHighlight = {
+      id: 'test-id',
+      verseId: 'verse-123',
+      color: 'blue',
+      createdAt: Date.now(),
+      updatedAt: Date.now(),
+      syncStatus: 'pending'
+    }
+    expect(['pending', 'syncing', 'synced', 'error']).toContain(highlight.syncStatus)
+  })
+})
diff --git a/types/index.ts b/types/index.ts
index 9e87d59..2dbc494 100644
--- a/types/index.ts
+++ b/types/index.ts
@@ -94,3 +94,33 @@ export interface CacheEntry {
   timestamp: number
   expiresAt: number
 }
+
+// Highlight system types
+export type HighlightColor = 'yellow' | 'orange' | 'pink' | 'blue'
+export type SyncStatus = 'pending' | 'syncing' | 'synced' | 'error'
+
+export interface BibleHighlight {
+  id: string // UUID
+  verseId: string
+  userId?: string // Optional, added by backend
+  color: HighlightColor
+  createdAt: number // timestamp
+  updatedAt: number // timestamp
+  syncStatus: SyncStatus
+  syncErrorMsg?: string
+}
+
+export interface HighlightSyncQueueItem {
+  highlightId: string
+  action: 'create' | 'update' | 'delete'
+  highlight: BibleHighlight
+  retryCount: number
+}
+
+export interface CrossReference {
+  refVerseId: string
+  bookName: string
+  chapter: number
+  verse: number
+  preview: string
+}