Mastic is a hamlet and a census-designated place (CDP) in the southeastern part of the town of Brookhaven in central Suffolk County, New York, United States.

The Long Island Rail Road built a station in 1882 and, on July 15, 1960, the stop was moved 7,010 feet (2,140 m) west and renamed Mastic–Shirley.

The Poospatuck Indian Reservation lies entirely within the community, near its southern end and along the Forge River.

The northernmost section of the hamlet is called Manor Park, which stretches from Sunrise Highway to Moriches-Middle Island Road immediately east of Brookhaven Airport.

Part of the neighborhood lies within the hamlet of Shirley, but is served entirely by Mastic's zip code of 11950.