Cape Cod is a peninsula extending into the Atlantic Ocean from the southeastern corner of mainland Massachusetts, in the northeastern United States. Its historic, maritime character and ample beaches attract heavy tourism during the summer months. The name Cape Cod, coined in 1602 by Bartholomew Gosnold, is the ninth oldest English place-name in the U.S.

As defined by the Cape Cod Commission's enabling legislation, Cape Cod is conterminous with Barnstable County, Massachusetts. It extends from Provincetown in the northeast to Woods Hole in the southwest, and is bordered by Plymouth to the northwest. The Cape is divided into fifteen towns, several of which are in turn made up of multiple named villages. Cape Cod forms the southern boundary of the Gulf of Maine, which extends north-eastward to Nova Scotia.

Since 1914, most of Cape Cod has been separated from the mainland by the Cape Cod Canal. The canal cuts 7 miles (11 km) roughly across the base of the peninsula, though small portions of the Cape Cod towns of Bourne and Sandwich lie on the mainland side of the canal. Two highway bridges cross the Cape Cod Canal: the Sagamore Bridge and the Bourne Bridge. In addition, the Cape Cod Canal Railroad Bridge carries railway freight and provides limited passenger service onto the Cape.