What is the name of the subway system in Boston, known as the 'T'?

The subway system in Boston is the MBTA subway, commonly known as “the T.” The name comes from the Massachusetts Bay Transportation Authority, the regional agency that operates Boston’s rapid-transit network.

The T is not a single uniform railway. It combines three heavy-rail lines—the Red, Orange, and Blue lines—with the light-rail Green and Mattapan lines and the Silver Line bus rapid-transit network. That mixture is why Boston’s system can look different from city to city: some routes use full-size metro trains, while others use street-running or surface light rail.

Boston’s transit history is especially old. The Tremont Street subway opened in 1897, making it the oldest subway tunnel in North America still in regular use. The system’s familiar color identities were introduced in 1965, replacing older route-numbering conventions.

A common mix-up is treating “the T” as only the underground trains. In everyday Boston usage, it can refer to the broader MBTA transit network, while “MBTA subway” more precisely identifies its rapid-transit services.