Haymarket station is an underground Massachusetts Bay Transportation Authority (MBTA) rapid transit station located at Haymarket Square in Boston, Massachusetts. It is a transfer station between the Green Line and Orange Line of the MBTA subway system, as well as a terminal for MBTA bus routes serving northern and northeastern suburbs. The two lines run parallel to each other through the station, with two side platforms for the Orange Line and a single island platform for the Green Line. The station is fully accessible.

The Green Line is a semi-metro system run by the Massachusetts Bay Transportation Authority (MBTA) in the Boston, Massachusetts, metropolitan area. It is the oldest MBTA subway line, and with tunnel sections dating from 1897, the oldest subway in North America. It runs underground through downtown Boston, and on the surface into inner suburbs via six branches on radial boulevards and grade-separated alignments. With an average daily weekday ridership of 137,700 in 2019, it is the third-most heavily used light rail system in the country. The line was assigned the green color in 1967 during a systemwide rebranding because several branches pass through sections of the Emerald Necklace of Boston.