Ball Square station is an under-construction light rail station on the Massachusetts Bay Transportation Authority (MBTA) Green Line located at Ball Square in Somerville and Medford, Massachusetts. The accessible station has a single island platform serving the two tracks of the Medford Branch. It is planned to open on December 12, 2022, as part of the Green Line Extension (GLX), which is adding two northern branches to the Green Line, and will be served by the E branch.