"M.T.A.", often called "The MTA Song", is a 1949 song by Jacqueline Steiner and Bess Lomax Hawes. Known informally as "Charlie on the MTA", the song's lyrics tell of a man named Charlie trapped on Boston's subway system, then known as the Metropolitan Transit Authority (MTA). The song was originally recorded as a mayoral campaign song for Progressive Party candidate Walter A. O'Brien. A version of the song with the candidate's name changed became a 1959 hit when recorded and released by the Kingston Trio, an American folk group.

The song has become so entrenched in Boston lore that the Boston-area transit authority named its electronic card-based fare collection system the "CharlieCard" as a tribute to this song. The transit organization, now called the Massachusetts Bay Transportation Authority (MBTA), held a dedication ceremony for the card system in 2004 which featured a performance of the song by the Kingston Trio and then-governor Mitt Romney.