Cape Breton Island (French: île du Cap-Breton—formerly Île Royale, Scottish Gaelic: Ceap Breatainn or Eilean Cheap Bhreatainn, Míkmaq: Únamakika, simply: Cape Breton) is an island on the Atlantic coast of North America. The name probably corresponds to the word Breton, the French adjective referring to the Atlantic province of Brittany.

Cape Breton Island is part of the province of Nova Scotia, Canada. The 10,311 km² (3,981 sq mi) island accounts for 18.7% of the total area of Nova Scotia. Although physically separated from the Nova Scotia peninsula by the Strait of Canso, it is artificially connected to mainland Nova Scotia by the 1,385 m (4,544 ft) long rock-fill Canso Causeway. The island is located east-northeast of the mainland with its northern and western coasts fronting on the Gulf of Saint Lawrence; its western coast also forming the eastern limits of the Northumberland Strait. The eastern and southern coasts front the Atlantic Ocean; its eastern coast also forming the western limits of the Cabot Strait. Its landmass slopes upward from south to north, culminating in the highlands of its northern cape. One of the world's larger salt water lakes, Bras d'Or ("Arm of Gold" in French), dominates the centre of the island.