The Maryland Transit Administration was originally known as the Baltimore Metropolitan Transit Authority, then the Maryland Mass Transit Administration before it changed to its current name in October 2001. The MTA took over the operations of the old Baltimore Transit Company on April 30, 1970.

Many routes of the agency's current bus lines are based on the original streetcars operated by the Baltimore Transit Company and its parent companies between the 1890s and 1960s. All of these routes were ultimately converted to rubber tire bus operations, and many were consolidated, extended into newly developed areas, or otherwise reconfigured to keep up with the ridership demands of the times. Additional routes and extensions were added in later years to serve newly developed communities and to feed into Metro and Light Rail stations.

With the growth in popularity of the private automobile during the 20th century, streetcar and bus ridership declined, and the needs for public transportation changed. Mass transit in Baltimore and other cities shifted from a corporate operation to a service funded and run by the government. The amount of service provided was greatly reduced. Some areas once served by streetcars are now served minimally by buses or not at all.

The demise of the Baltimore streetcar took place between the years of 1947 and 1963, hastened by National City Lines' acquisition, which said that buses offered lower maintenance and had greater flexibility in traffic. With its rails demolished, Baltimore was no longer a streetcar city. As transit needs and trends changed, rail transit did return to the city, with the Metro Subway opening in 1983 and the Light Rail in 1992.

The track gauge was 5 ft 4+1⁄2 in (1,638 mm). This track gauge is now confined to the Baltimore Streetcar Museum.

The following bus companies operated many of the services later provided by the Maryland Transit Administration:

The Baltimore Transit Company (BTCO) was a privately owned public transit operator that provided streetcar and bus service in Baltimore from 1935. It was the successor to the old United Railways and Electric Company, formed in 1899 to consolidate and operate Baltimore's streetcar lines. The company was purchased in 1948 by National City Lines and the streetcar system was then run down in favor of buses, a process repeated in many places, which became known as the Great American Streetcar Scandal. The last streetcar ran in 1963. Between 1940–1959, Baltimore Transit also operated trolley buses (or "trackless trolleys") on six lines, including Howard Street and Federal Street.

BTCO was absorbed by what is now the Maryland Transit Administration in 1970. The BTC oversaw the elimination of streetcar service in favor of bus service in 1963 when the last streetcar routes, the number 8 providing service from Catonsville to Towson and the number 15 (Overlea to Walbrook Junction) were eliminated on November 3, 1963.