The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional municipal authority (Municipal authority (Pennsylvania)) that operates various forms of public transit ? bus (transit bus), subway (Rapid transit) and elevated (elevated railway) rail, commuter rail, light rail, and electric trolley bus (trolleybus) ? that serve 3.8 million people in and around Philadelphia, Pennsylvania. SEPTA also manages construction projects that repair, replace, and expand infrastructure and rolling stock.

SEPTA serves the combined city and county of Philadelphia, Delaware County (Delaware County, Pennsylvania), Montgomery County (Montgomery County, Pennsylvania), Bucks County (Bucks County, Pennsylvania), and Chester County (Chester County, Pennsylvania). SEPTA also serves New Castle County (New Castle County, Delaware) in Delaware, and Mercer County (Mercer County, New Jersey) in New Jersey.

SEPTA has the 6th-largest U.S. transit system (List of United States rapid transit systems by ridership) by ridership, with about 306.9 million annual unlinked trips. It controls 280 active stations, over 450 miles of track, 2,295 revenue vehicles, and 196 routes. SEPTA also manages Shared-Ride services in Philadelphia and ADA (Americans with Disabilities Act of 1990) services across the region. These services are operated by third-party contractors.

SEPTA is one of only two U.S. transit agencies that operates all of the five major types of transit vehicles: regional (commuter) rail trains, "heavy" rapid transit (subway/elevated) trains, light rail vehicles (trolleys), electric trolleybuses and motor buses. The other is Bostons Massachusetts Bay Transportation Authority (which runs ferryboat service as well).

SEPTA employs more than 9,000 people. Its headquarters is located at 1234 Market Street (Market Street (Philadelphia)) in Center City Philadelphia.