The MBTA Commuter Rail system serves as the commuter rail arm of the Massachusetts Bay Transportation Authority's (MBTA's) transportation coverage of Greater Boston in the United States. Trains run over 394 mi (634 km) of track to 134 stations. It is operated under contract by Keolis, which took over operations on July 1, 2014, from the Massachusetts Bay Commuter Railroad Company (MBCR).

The Massachusetts Bay Transportation Authority is the public agency responsible for operating most public transportation services in Greater Boston, Massachusetts. The MBTA transit network includes the MBTA subway with three metro lines, two light rail lines, and a five-line bus rapid transit system ; MBTA bus local and express service; the twelve-line MBTA Commuter Rail system, and several ferry routes. In 2023, the system had a ridership of 239,981,700, or about 755,500 per weekday as of the fourth quarter of 2023, of which the rapid transit lines averaged 267,100 and the light rail lines 80,300, making it the fourth-busiest rapid transit system and the third-busiest light rail system in the United States. As of the fourth quarter of 2023, average weekday ridership of the commuter rail system was 97,100, making it the fifth-busiest commuter rail system in the U.S.