Stockholm commuter rail (Swedish: Stockholms pendeltåg) is the commuter rail system in Stockholm County, Sweden. The system is an important part of the public transport in Stockholm, and is controlled by Storstockholms Lokaltrafik. The tracks are state-owned and administered by the Swedish Transport Administration, while the operation of the Stockholm commuter rail services itself has been contracted to SJ AB since March 2024.

Local trains have been operated on the mainline railways around Stockholm since the late nineteenth century. At the beginning, local rail services were part of the Swedish State Railways, but in the late-1960s, the responsibility for these services was transferred to Stockholm County, which incorporated it with the ticketing system of Stockholm Transport. New trains were bought, stations were modernised, and the Stockholm commuter rail network was developed with an aim of making it more metro-like. Originally the system was branded as SL förortståg (English: SL suburban train), and later as SL lokaltåg (English: SL local/commuter train). Only in the 1980s did the system officially become known as Stockholms pendeltåg.

In its first year of operation there was only one route which went from Södertälje södra (now Södertälje Hamn) to Kungsängen via Stockholm Central Station. On 1 June 1969, the system was extended to Märsta via a branch located after Karlberg Station [sv] and a new service was created in which trains on the Kungsängen branch terminated at Stockholm C instead. In 1975 another branch line opened to Västerhaninge, with a single-track shuttle service to Nynäshamn. Trains on the Kungsängen branch now terminated at Västerhaninge instead of Stockholm C and which now forms part of the modern Line 43.

From 1986 until 1996, important improvements were made to the railways around Stockholm. Single-track stretches were upgraded to double tracks, and some double-track stretches were upgraded to four-track, allowing the commuter trains to run with less interference from other rail services. The service frequency was gradually increased, and from 2001 most stations on the network are served by trains at regular 15-minute intervals, with additional trains during rush hours.

In 2001, the northwestern arm of the network was extended from Kungsängen to Bålsta. A southern infill station at Årstaberg was inaugurated in 2006, in order to connect with the then new Tvärbanan tram system. A new station at Gröndalsviken opened on the southeastern Västerhaninge-Nynäshamn shuttle on 18 August 2008.

Since 9 December 2012, it has been possible for Stockholm commuter rail trains to stop at Stockholm Arlanda Airport. Journeys take 38 minutes from Arlanda C station to Stockholm C, and 18 minutes from Arlanda C to Uppsala C. Discussions on the expansion began in December 2007. The airport has had express service from Stockholm Central through Arlanda Express since 1999, and was also reachable by bus from Märsta station. The implementation required negotiations between Stockholm Transport and Arlanda Express, who had operating rights for the tracks.

A rail tunnel underneath central Stockholm began construction in 2008 and opened on 10 July 2017. This new tunnel, known as Stockholm City Line (Citybanan; lit. ‘the city line’), is intended for the exclusive use of the Pendeltåg system, and splits commuter traffic onto separate tracks from long-distance trains while travelling through the city. This eases the rail systems' congestion problems, and permits Stockholm Transport to schedule more frequent service. It also allows more frequent service for other trains, increasing the capacity for large parts of the Swedish rail network since many trains go to and from Stockholm. Two new underground stations, Stockholm City Station (located under T-Centralen, both stations with connections to Stockholm Central Station) and Stockholm Odenplan station; located under Odenplan metro station, replacing Karlberg Station) were built as part of the Citybanan project.

A new station called Vega, located on the Nynäs Line in Haninge Municipality between Skogås and Handen stations, opened on 1 April 2019 after almost four years of construction. Vega was also the name of a small halt on the Nynäs Line which existed between 1929 and 1973, although it was built at a different location from the current Vega station.