The Massachusetts Bay Transportation Authority (MBTA), commonly known as 'The T,' is the primary public agency responsible for operating most public transportation services in Greater Boston, Massachusetts. Established in 1964 under Chapter 161A of the Massachusetts General Laws to consolidate and modernize fragmented private transit operations dating back to the 19th century, it is one of the oldest public transit systems in the United States. As a division of the Massachusetts Department of Transportation (MassDOT) since 2009, the MBTA manages a comprehensive network that includes three subway lines (Red, Orange, and Blue), two light rail lines (Green and Mattapan), a bus rapid transit system with five lines, extensive local and express bus services, a twelve-line commuter rail system, and several ferry routes serving eastern Massachusetts and parts of Rhode Island. The agency also offers paratransit services for people with disabilities. In 2024, the MBTA system recorded a ridership of 245,498,400, averaging about 864,400 passengers per weekday as of the third quarter of 2025, positioning it as the fourth-busiest rapid transit system and third-busiest light rail system in the United States, with the commuter rail averaging 100,200 weekday riders, making it the fifth-busiest in the country. The MBTA plays a crucial role in regional mobility, supporting daily commutes, tourism, and economic activity in the densely populated Boston metropolitan area. The agency has been a defendant in several high-profile free speech cases involving advertising policies on its vehicles and stations, highlighting tensions between public transit operations and First Amendment rights. The MBTA continues to invest in improvements like electrification and accessibility upgrades, though it has faced ongoing challenges related to infrastructure maintenance, funding, expansion, service reliability, and safety concerns in recent years.