Sullivan Square station is a rapid transit station on the MBTA subway Orange Line, located adjacent to Sullivan Square in the Charlestown neighborhood of Boston, Massachusetts. It is a major transfer point for MBTA bus service, with 12 routes using a two-level busway. The station has two island platforms serving the two active Orange Line tracks plus an unused third track. The Haverhill Line and Newburyport/Rockport Line pass through the station on separate tracks but do not stop.

The Orange Line is a rapid transit line operated by the Massachusetts Bay Transportation Authority (MBTA) as part of the MBTA subway system. The line runs south on the surface from Oak Grove station in Malden, Massachusetts through Malden and Medford, paralleling the Haverhill Line, then crosses the Mystic River on a bridge into Somerville, then into Charlestown. It passes under the Charles River and runs through Downtown Boston in the Washington Street Tunnel. The line returns to the surface in the South End, then follows the Southwest Corridor southwest in a cut through Roxbury and Jamaica Plain to Forest Hills station.