The Market–Frankford Line (MFL), or the Blue Line) is one of three rapid transit lines in Philadelphia, Pennsylvania; it and the Broad Street Line are operated by SEPTA, and the PATCO Speedline is operated by PATCO. The Market–Frankford Line runs from the 69th Street Transportation Center in Upper Darby, just outside of West Philadelphia, through Center City Philadelphia to the Frankford Transportation Center in Near Northeast Philadelphia. From 2024 onwards, this line will be rebranded as the L line.

The 69th Street Transportation Center is a SEPTA terminal in the Terminal Square section of Upper Darby Township, Pennsylvania. It serves the Market–Frankford Line, Norristown High Speed Line, and SEPTA Routes 101 and 102 trolleys, and multiple bus routes. It is located at the end of 69th Street, a major retail corridor in Upper Darby Township across Market Street from the Tower Theater. Until 2011, the station was primarily known as 69th Street Terminal.