Chappaquiddick Island is a peninsula and occasional island off the eastern end of Martha's Vineyard. Norton Point, a narrow barrier beach, connects Martha's Vineyard and Chappaquiddick between Katama and Wasque. Breaches occur due to hurricanes and strong storms separating the islands for periods of time. The two islands most recently reconnected on December 31, 2023. While both land forms have mostly been connected to one another in modern history, Chappaquiddick is nevertheless referred to as an island.

Martha's Vineyard, often simply called the Vineyard, is an island in the U.S. state of Massachusetts, lying just south of Cape Cod. It is known for being a popular, affluent summer colony, and includes the smaller peninsula Chappaquiddick Island. It is the 58th largest island in the U.S., with a land area of about 96 square miles (250 km2), and the third-largest on the East Coast, after Long Island and Mount Desert Island. Martha's Vineyard constitutes the bulk of Dukes County, Massachusetts, which also includes the Elizabeth Islands and the island of Nomans Land.