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. Those followed from horsecar railway companies which had laid track along Baltimore streets beginning in 1859; many lines followed old turnpike roads and connected the city's neighborhoods with suburban villages. 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 . This track gauge is now confined to the Baltimore Streetcar Museum.

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

Baltimore Transit Company 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.

In the midst of the Civil Rights Movement, the BTCO fired a white bus driver who claimed to be the Grand Wizard of the Baltimore Ku Klux Klan. A labor arbitrator ruled in favor of BTCO in this firing, which was in part spurred by other white drivers threatening to strike if the man was not dismissed.

Old Court Bus Lines Old Court Bus Lines was a service that provided van transport in northwest Baltimore County. Its lines served places including Stevenson and Villa Julie College. These services have been provided by MTA since 1973, though much of them have been cut back or modified. Bus Route 60 serves Stevenson University, which used to be known as Villa Julie.

Rosedale Passenger Lines Operated service in eastern Baltimore County. Most of its services later became a part of Bus Route 23. The only one still provided by MTA is service to Victory Villa, on Route 4.

Dundalk Bus Lines Dundalk Bus Lines provided service in various parts of southeast Baltimore County between 1940 and 1972. MTA serves some of these areas with Bus Route 4.

McMahon Services Operated in northeast Baltimore County to locales such as Lutherville and Jacksonville. The only route incorporated by MTA was Route 19A, which later became known as Route 105. Discontinued in 2005.

Job Express Transit Operated several routes during the 1960s. Most notably, Route H became known as the #7 Rosewood Express serving Rosewood Center for more than 30 years. The #7 Rosewood Express service ultimately became Route 102 in 2000, and was absorbed by Route M-17 in 2005. Route M-17, along with this service, was eliminated in 2009.

Auxiliary Bus Lines Operated some of the routes around the city, such as what is now Route 51.

Baltimore Streetcar Museum A track providing service at the Baltimore Streetcar Museum was designated in 1970 as Route 25, and was renamed LocalLink 25 in June 2017.

June 2017 Bus Redesign There was a bus redesign in June 2017 called BaltimoreLink.

Local routes prior to June 2017 RouteTerminusDivision OperationMajor StreetsPlaces ServedCorridor LineReplaced byRoute 1 Sinai Hospital (NB) Mondawmin station (NB) Fort McHenry (SB) Bush Street (1) Greenspring Ave Fulton Ave Fort Ave Coldspring-Newtown Druid Hill Park Mondawmin Sandtown-Winchester Baltimore Arena Inner Harbor Federal HillGreenspring Ave/Fulton Ave-Fort McHenry LineLocalLink 91, 94CityLink NavyRoute 3 Cromwell Bridge Rd Park & Ride (NB) Sheppard Pratt (NB) Taylor Avenue (NB) Inner Harbor (SB) Bush Street (1)Kirk Avenue (3) Loch Raven Blvd 33rd St Charles St St. Paul St Loch Raven Eudowood Ramblewood Good Samaritan Hospital Union Memorial Hospital Waverly Johns Hopkins University Charles Village Penn Station Mt. Vernon Enoch Pratt Free Library Baltimore ArenaCharles St-33rd St-Loch Raven Blvd LineCityLink Silver, GreenLocalLink 53Route 4 CCBC Essex (NB) Turner's Station (SB) Eastern (2) Rossville Blvd Eastern Ave North Point Rd Wise Av Franklin Square Hospital Center Golden Ring Plaza Middle River Essex Eastpoint Mall CCBC Dundalk North Point DundalkDundalk-Eastern Ave-Essex LineLocalLink 62Route 5 Mondawmin station (WB) Federal Street (EB) Cedonia (EB) Eastern (2)Northwest (4) Druid Hill Ave/McCulloh St Eutaw St Fayette/Baltimore St Federal St Sinclair Ln Reservoir Hill Madison Park Lexington Market Baltimore Arena Johns Hopkins Hospital Collington Square MoraviaDruid Hill-Sinclair Ln LineCityLink Yellow, Purple, PinkRoute 7 Mondawmin station (WB) Canton (EB) Eastern (2)Northwest(4) Pennsylvania Ave Paca/Greene St Pratt/Lombard St Upton UMB Oriole Park Inner Harbor National Aquarium Little Italy Butcher's Hill Patterson ParkPennsylvania Ave-Canton LineLocalLink 65, 73CityLink LimeRoute 8 Lutherville station (NB) North Ave (NB) (SB) Selected Trips UMB Transit Center (SB) Bush Street (1)Kirk Avenue (3) Greenmount Ave/York Rd Fayette/Baltimore St Goucher College Towson Town Center Towson Towson University Belvedere Square Senator Theater Govans Waverly First Mariner ArenaGreenmount Ave-York Rd LineCityLink RedRoute 9 Lutherville station (NB) International Circle (SB) Kirk Avenue (3) York Rd Deereco Rd Warren Rd McCormick Rd Timonium station Timonium Fairgrounds Cockeysville Warren Road station McCormick Industrial Park Hunt Valley Town CenterHunt Valley LineLocalLink 93Route 10 Catonsville (WB) Dundalk & Center Pl (EB) Bullneck (EB) Bush Street (1)Eastern (2) Frederick Rd Pratt/Lombard St Eastern Ave Dundalk Ave Yale Heights Pigtown B&O Railroad Museum Inner Harbor National Aquarium Little Italy Fells Point Patterson Park Highlandtown Turner's StationFrederick Ave-Eastern Ave LineCityLink Purple, NavyRoute 11 Towson Town Center (NB) Bedford Square (NB) Inner Harbor Layover (SB) Kirk Avenue (3) Charles St Bellona Ave Pratt/Lombard St Towson Courthouse Towson University Rodgers Forge Homeland Loyola College NDMU Johns Hopkins University Baltimore Museum of Art Charles Village Penn Station Mt. Vernon Washington Monument Baltimore Arena Convention Center Inner HarborCharles St LineLocalLink 51Route 12 Kirk Avenue Division (SB) Stella Maris (NB) Kirk Avenue (3) Greenmount Ave/York Rd Dulaney Valley Rd Towson Hampton Goucher CollegeGreenmount Ave-York Rd LineLocalLink 52Route 13 Walbrook Junction (WB) North Ave & Patterson Park Ave (EB) Canton (EB) Eastern (2)Northwest (4) North Ave Washington/Wolfe St Coppin State College Johns Hopkins Hospital Penn-North station North Avenue station Great Blacks in Wax Museum(Crosstown)North Ave-Canton LineCityLink GoldLocalLink 21Route 14 Patapsco station (NB) Jumpers Hole (SB) Annapolis (SB) Bush Street (1) Patapsco Ave Ritchie Hwy Crain Hwy Baltimore-Annapolis Blvd Brooklyn Park Glen Burnie Harundale Pasadena Severna Park MVA Headquarters Cromwell station (now Glen Burnie) Arundel Medical Center Marley Station Mall AACC U.S. Naval AcademyRitchie Hwy LineLocalLink 69, 70Route 15 Security Square Mall (WB) Walbrook Junction (WB) Westview Mall (WB) Rutherford Business Park (WB) Gardenville (EB) Overlea (EB) Perry Hall (EB) Bush Street (1)Kirk Avenue (3) Security Blvd Windsor Mill Rd Forest Park Ave Poplar Grove St Edmondson Ave Saratoga St Belair Rd Social Security Woodlawn Lorraine Kernan Hospital Forest Park Rosemont Belair-Edison Gardenville FullertonWindsor Hills-Saratoga St-Belair Rd LineCityLink BrownLocalLink 34, 79, 80Route 16 Mondawmin station (NB) Brooklyn (SB) Bush Street (1)Northwest (4) Hilton Street Caton Avenue Patapsco Avenue Coppin State College Rosemont Violetville Patapsco station(Crosstown)Patapsco Ave LineLocalLink 29Route 17 Patapsco station (NB) BWI Airport (SB) Arundel Mills (SB) Parkway Center (SB) Bush Street (1) Annapolis Rd Nursery Rd Aviation Blvd Route 100 Nursery Road station Linthicum BWI Airport BWI Business District BWI Rail Station Arundel Mills HanoverNursery Rd-BWI Airport LineLocalLink 75Route 19 Carney (NB) Goucher & Taylor (NB) State Center station (SB) Bush Street (1)Kirk Avenue (3) Gay St Harford Rd Hillsway/Northern Pkwy McLean Blvd Montebello State Hospital Hamilton Parkville HillendaleHarford Rd LineLocalLink 54Route 20 Security Square Mall (WB) Edmondson Village (WB) City Hall (EB) Bush Street (1)Eastern (2) Fayette/Baltimore St Old Frederick Rd Crosby Rd Rolling Rd Gay St Woodlawn Westview Mall Westview Edmondson Village Grace Medical Center Baltimore Arena City HallBaltimore St/Fayette St LineCityLink GreenLocalLink 78Route 21 Mondawmin station (WB) Fells Point (EB) Eastern (2) Gilmor St Dolphin St Preston/Biddle St Caroline St Sandtown-Winchester Mt. Royal State Center station Meyerhoff Symphony Hall MICA University of Baltimore Sojourner-Douglass College(Crosstown)Sandtown-Preston/Biddle Streets-Caroline St LineCityLink Lime, Pink, NavyRoute 22 Mondawmin station (WB) Highlandtown (EB) Bayview Medical Center (EB) Eastern (2)Northwest (4) University Pkwy 33rd St Erdman Ave Edison Hwy Highland Ave Eastern Ave BCCC Liberty Campus Druid Hill Park Television Hill Hampden Johns Hopkins University Waverly Highlandtown Union Memorial Hospital(Crosstown)42nd St-Highland Ave LineLocalLink 22Route 23 Catonsville (WB) Wildwood (WB) Fox Ridge (EB) Bush Street (1)Eastern (2) Edmondson Avenue Franklin/Mulberry St Saratoga St Fayette/Baltimore St Eastern Ave Allendale Rosemont West Baltimore station Baltimore Arena Shot Tower Patterson Park Bayview Medical Center Eastpoint Essex Park & Ride lotEdmondson Ave-Eastern Ave-Fox Ridge LineLocalLink 77CityLink Blue, OrangeRoute 24 Moravia (WB) Whispering Woods (EB) Eastern (2) Eastern Blvd Sinclair Ln Martin State Airport