Cape Breton Island (French: île du Cap-Breton, formerly île Royale; Scottish Gaelic: Ceap Breatainn or Eilean Cheap Bhreatainn; Miꞌkmaq: Unamaꞌki) is an island on the Atlantic coast of North America and part of the province of Nova Scotia, Canada.

The 10,311 km² (3,981 sq mi) island accounts for 18.7% of Nova Scotia's total area. Although the island is physically separated from the Nova Scotia peninsula by the Strait of Canso, the 1,385 m (4,544 ft) long Canso Causeway connects it to mainland Nova Scotia. The island is east-northeast of the mainland with its northern and western coasts fronting on the Gulf of Saint Lawrence with its western coast forming the eastern limits of the Northumberland Strait. The eastern and southern coasts front the Atlantic Ocean with 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 saltwater lakes, Bras d'Or ("Arm of Gold" in French), dominates the island's centre.

The total population at the 2016 census numbered 132,010 Cape Bretoners, which is approximately 15% of the provincial population. Cape Breton Island has experienced a decline in population of approximately 2.9% since the 2011 census. Approximately 75% of the island's population is in the Cape Breton Regional Municipality (CBRM), which includes all of Cape Breton County and is often referred to as Industrial Cape Breton.