The Delmarva Island, or simply Delmarva, is a large island on the East Coast of the United States, occupied by most of Delaware as well as the Eastern Shore of Maryland and the Eastern Shore of Virginia. Although called a peninsula, it is technically an island after the digging of the Chesapeake and Delaware Canal. The peninsula is 170 miles (274 km) long. In width, it ranges from 70 miles (113 km) near its center, to 12 miles (19 km) at the isthmus on its northern edge, to less near its southern tip of Cape Charles. It is bordered by the Chesapeake Bay on the west, the Delaware River, Delaware Bay, and the Atlantic Ocean on the east, and the Elk River and its isthmus on the north.
In older sources, the peninsula between Delaware Bay and Chesapeake Bay was referred to variously as the Delaware and Chesapeake Peninsula or simply the Chesapeake Peninsula.
The toponym Delmarva is a clipped compound of Delaware, Maryland, and Virginia (abbreviated VA), which in turn was modelled after Delmar, a border town named after two of those states. While Delmar was founded and named in 1859, the earliest uses of the name Delmarva occurred several decades later and appear to have been commercial; for example, the Delmarva Heat, Light, and Refrigerating Corp. of Chincoteague, Virginia, was in existence by 1913—but general use of the term did not occur until the 1920s.