Chappaquiddick Island (; Massachusett language: Noepetchepi-aquidenet; colloquially known as "Chappy"), a part of the town of Edgartown, Massachusetts, is a small island off the eastern end of Martha's Vineyard. Norton Point, a narrow barrier beach, sometimes 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, most recently on December 22, 2022. While both land forms have mostly been connected to one another in modern history, Chappaquiddick is nevertheless referred to as an island.

Visitors come to the isolated island for beaches, cycling, hiking, nature tours and birding, and the MyToi Gardens, a small Japanese garden created amidst the native brush. Two fire trucks are stationed on the island from Edgartown. Chappaquiddick Road and Poucha Road, both paved, provide access to sandy, woodland roads, trails, and shorelines.

Chappaquiddick became internationally known following an incident of the same name in 1969, when U.S. Senator Ted Kennedy accidentally drove his car off the island's Dike Bridge into Poucha Pond. Kennedy's 28-year-old passenger, Mary Jo Kopechne, drowned inside the car.