The SEPTA Regional Rail system (reporting marks SEPA, SPAX) consists of commuter rail service on thirteen branches to over 150 active stations in Philadelphia, Pennsylvania, United States and its suburbs. Service on most lines runs from 5:30 AM to midnight. The core of the Regional Rail system is the Center City Commuter Connection composed of three Center City stations in the "tunnel" corridor: the above-ground upper level of 30th Street Station; and the underground Suburban Station; and Market East Station. All trains stop at these Center City stations, and most also stop at Temple University station on the campus of Temple University in North Philadelphia. Operations are handled by the SEPTA Railroad Division.

The 13 branches can be divided into those originally owned and operated by the Pennsylvania Railroad (PRR) (which would become Penn Central), and those of the Reading Company (RDG). Before the Center City Commuter Connection opened in November 1984, the Pennsylvania Railroad commuter lines and the Reading commuter lines were two completely separate railroads. Each had a separate Center City terminal, with the PRR lines terminating at Suburban Station, while the RDG lines terminated at Reading Terminal.

Regional rail is passenger rail transport services that operate between towns and cities. It operates with more stops and lower distances than does inter-city rail, but fewer stops and faster than commuter rail. Other terms include local train and stopping train. Regional rail operate beyond the limits of urban areas, and either connect similarly sized smaller cities and towns, or connect cities to the surrounding towns, outside or at the outer rim of the suburban belt.

Regional rail normally operates with an even service load throughout the day, although slightly increased services may be provided during rush-hour. The service is less oriented around bringing commuters to the urban centers, although this may generate part of the traffic on some systems. Other regional rail services operate between two large urban areas, but make many intermediate stops.

The main difference between regional rail and commuter rail is that the latter is focused on moving people between where they live and where they work on a daily basis. Regional rail operates outside major cities. Unlike inter-city, it stops at most or all stations. It provides a service between smaller communities along the line, and also connections with long-distance services. Regional rail typically operates throughout the day but often at low frequency (once per hour or only a few times a day), whereas commuter rail provides a high-frequency service within a conurbation.