[8] The Stockholm metro has been referred to as 'the world’s longest art gallery,' featuring decorations at more than 90 of its 100 stations, including sculptures, rock formations, mosaics, paintings, light installations, engravings, and reliefs created by over 150 artists.

[9] In the late 19th century, Stockholm’s suburbs expanded thanks to the development of local railways such as Djursholmsbanan and Saltsjöbanan.

With further suburbs planned, it became evident that trams would not meet the city's future transport needs,[12] prompting underground railway proposals.

Stockholm's politicians were also inspired by large cities such as London, Paris and New York where metros had already been built.

[20] The 1930s also brought significant changes to the political and economic landscape of housing construction in Stockholm, with a new municipal plan for multi-family dwellings in the suburbs.

[21] In 1941, Stockholm City Council voted to develop a large-scale metro system, based on plans from the 1930 Traffic Committee and a further 1940 report.

Several of the stations (especially on the Blue Line) are left with the bedrock exposed, crude and unfinished, or as part of the decorations..[27] The following details relate to the present network.

It is 41.238 kilometres (25.624 mi) long (only 18 metres (59 ft) shorter than the Green line), and was opened on 5 April 1964.

It was opened on 31 August 1975 and is used by 171,000 passengers per workday or 55 million per year (2005).Trains operate from 05:00 to 01:00, with extended all night service on Fridays and Saturdays.

As a result, ten-car trains only operated on the Blue Line, where most platforms (except at Husby) were designed to accommodate their length.

As a result, ten-car trains were never used in service on the Red Line, except at the six stations between Stadion and Mörby Centrum, which could accommodate them.

Compared to previous stock, the cars have fewer seats arranged in mixed longitudinal/transverse layout for increased capacity, similar to the C1 and refurbished C20 trains.

[39] The C30 is the first full Stockholm metro train type to feature air-conditioning in both the passenger compartments and driver's cabs and are expected to cost 5 billion kronor.

The signal is picked up from the rail tracks through two antennas placed in front of the first wheel axle and compared with data about the train's speed.

The signalling system on the Red Line was supposed to be replaced with a Communications-based train control (CBTC) system manufactured by Ansaldo STS under a contract awarded by SL in 2010, however SL cancelled said contract in 2017, reportedly after repeated delays in project implementation.

In recent years, stricter zero-tolerance policies have been implemented, with graffiti-covered trains immediately removed from service and station graffiti cleaned within 24 hours.

[45] SL also introduced new measures, including fencing, radar-equipped surveillance cameras, and rapid cleaning protocols.

[50] Advocacy for art on the metro was driven by artists Vera Nilsson and Siri Derkert, who faced resistance from officials and politicians who questioned its relevance and cost.

[51] However by 1957, Stockholm City Council had approved the integration of art into the metro, and established a program to commission works for new stations, starting with T-Centralen.

[52] The first major art installations in the Stockholm metro appeared in the 1960s, with Siri Derkert's 1965 work at Östermalmstorg Station, featuring sandblasted engravings focused on feminism, world peace, and environmentalism.

In the 1970s, as the metro expanded, including with the opening of the Blue Line, large-scale, immersive artworks became common.

Artists collaborated closely with architects, as seen at Solna Centrum (1975), where Anders Åberg and Karl-Olov Björk created a red and green cave-like design addressing urbanisation and environmental issues.

[53] In the 1980s and 1990s, the art program diversified, with stations like Kungsträdgården (designed by Ulrik Samuelson) incorporating historical motifs and archaeological elements.

In 2017, Liv Strömquist’s temporary exhibition The Night Garden at Slussen station featured sketches depicting subjects such as menstruation.

These new works are developed in close collaboration with architects and engineers, and often respond to the specific context of each station, reflecting local history, culture, or natural surroundings.

For example at Barkarbystaden station, Helena Byström’s work incorporates dynamic video art that references the area’s military aviation history.

[57]The modern railway network, which was inaugurated in 1950, has racked up several mythical urban legends over the years, notably involving ghost phenomena, especially of the horror genre.

[60] Another notable urban legend, especially in connection with the Silver Train, surrounds the unfinished Kymlinge metro station, which was built but never taken into service.

[62] In 2017, another agreement was reached regarding several public transportation projects in Stockholm, including a fourth metro line.

[68] To support the expansion of the Stockholm Metro, the Högdalen depot is being extended with new underground staging areas to service trains on both the Blue and Green lines.