The network expanded rapidly during the early decades of the 20th century; by 1944, its main routes were completed, with the addition of its newest line occurring as late as 2007.

A system of public water and sewage was first completed in 1886 and expanded in the subsequent decades, and many streets were paved as part of this same urban renewal.

[10] The Subte then entered into a concession model in the mid-1990s through which private sector parties were to submit bids to execute investment plans "designed and funded" by the state, while implemented by the concessionaire.

[22] By the 1920s, the Argentine government was dissatisfied with the lack of progress the AATC (which enjoyed a near-monopoly on the city's tramways by this point) had made in expanding the rest of the network and thus revoked its right to build any more lines in 1930, seeking instead another company to do so.

SBASE (as part of the Government of the City of Buenos Aires) maintained ownership of the network, its rolling stock, and infrastructure, and administers its expansion and budget.

[34] The relationship between Mauricio Macri's mayoral administration and Metrovías became increasingly strained, with the Government of Buenos Aires issuing multiple fines to the operator.

[34] The relationship was further strained in 2013 when Metrovías' 20-year concession ended and has since been renewed on a year-by-year basis, leaving the door open for a state-run or mixed operation.

[35] Among the public, privatisation has proved unpopular, with a survey carried out in 2015 indicating that 82% of passengers would like the Underground to be operated by the state instead of a private company.

[41][42] The current contract expired on 31 December 2019 with bids put forward by:[43][44] The network comprises six underground lines, labelled "A" to "E" and "H" and which are further identified by different colours, covering a total route length of 56.7 kilometers (35.2 mi) and serving 90 stations.

While tokens have been used in the past, at present riders use contactless cards called SUBE, which are rechargeable with multiple forms of payment.

[41] Trains originally ran until 01:00 am, but following the privatisation of the service through concession to Metrovías, the company established an earlier closing time of 23:00 in 1994 to carry out works on the lines.

These proposals have been rejected by Subterráneos de Buenos Aires, which stated in 2015 that the reduced schedule is needed in order to carry out infrastructure modernisation works across all the lines while they are closed.

[63] Current expansion efforts seek to not necessarily go through Plaza de Mayo by creating more north–south lines and moving termini away from the city centre.

If built, the new lines would mean that more than two million inhabitants of Buenos Aires (accounting for about 70% of the city centre's population) will live within 400 metres of a metro station.

Some criticisms include the failure of the PETERS plan to account for the extension of the Belgrano Sur Line to Constitucion railway station, meaning that Line C's extension to the minor Buenos Aires terminal would be redundant, and that the Retiro Norte node would also be made redundant by the planned Red de Expresos Regionales commuter rail tunnels which are to link the three major railway terminals of the city.

There are also several "digital spaces" across the network and in its commercial galleries where seating areas are provided, along with recharging stations for mobile devices.

[82] The Buenos Aires Underground has had among the longest serving and most varied rolling stock in the world, in part due to the network having been originally built and operated by three different companies in its early years, causing incompatibilities between the lines.

[91] The Buenos Aires Underground has historically been characterised by murals and other artistic works in its stations, making it a kind of museum throughout the system.

These works, and a number of complete stations, are considered part of the cultural heritage of the city and several of them were declared National Historic Landmarks in 1997.

[5][94][95] In March 2013, La Brugeoise subway carriages were replaced by new Chinese 200 Series rolling stock, just 11 months prior to their 100th anniversary on the line.

[98] During the festivities of the 100th anniversary of the underground on 1 December 2013, many restored La Brugeoise trains circulated Line A and there was a symphonic orchestra at Plaza de Mayo station as well as free rides for the entire city in order to mark the event.

[100][101] Currently, the Polvorín Workshop – originally inaugurated along with Line A – is being transformed into a museum to display artefacts and the former rolling stock of the Underground.

[102][103] The workshop also serves as the headquarters for the Association of Friends of the Tramway and many of the Underground's historical artefacts are stored there, such as the wooden UEC Preston "palace cars", which also make appearances on Line A during special occasions such as anniversaries and even the inauguration of president Raúl Alfonsín in 1983, where he and other officials were transported from the National Congress to the Casa Rosada using these cars.

[107][108] Featured artists include painters and reproductions by Quino, Molina Campos, Raúl Soldi, Rodolfo Medina and Jorge Schwarz.

Many of these artworks were painted directly over tiles dating back to the 1930s when the line was opened by the Lacroze company, while others were completely removed and destroyed.

[121] Recently opened Correo Central station has received an award from the Association of Structural Engineers in Argentina for the quality and creativity of the work.

Their houses were subsequently raided, uncovering a vast collection of stolen Subte paraphernalia as well as documented evidence of their activities in the form of videos and photographs.

[134] In January 2016, a group called Soketes Calcetines was discovered to be offering tourists graffiti tours of the Underground, giving them a chance to paint cars for a fee.

[63] One of Jorge Luis Borges' earlier editorial jobs was for Urbe, a promotional magazine for the underground system, which was privately owned at that time.

El Eternauta is a science fiction comic book created by Héctor Germán Oesterheld and Francisco Solano López in 1957.