Lanoel Aussenac d'Abel and Abel Coelho presented theirs in 1923, and José Manteca Roger and Juan Luque Argenti theirs one year later, in 1924.

[5] After World War II, in which Portugal remained neutral, the national economy took off and the financial possibilities arising from the Marshall Plan provided a strong boost to the potential construction of a metro in Lisbon.

The network was formed by a Y-shaped line linking Restauradores to Rotunda (now Marquês de Pombal), branching then to Entre Campos and to Sete Rios (now Jardim Zoológico), where the rolling stock depot (PMO I) which was also linked to the outer-loop Cintura Line of CP was located.

The metro has proved an important factor in urban development of the city, outlining new areas of housing and services.

In 1974, after the Carnation Revolution, the management model was changed, being nationalized in 1975 and renamed Metropolitano de Lisboa, EP in 1978.

It recommended that the Metro should operate the following routes by 1999: The PMO II depot at Campo Grande was finished in the autumn of 1994 after eleven years of works.

This line was 5 km (3.1 mi) long and included five new stations: Alameda II, Olaias, Bela Vista, Chelas, and Oriente; the line began running six car trains beginning in June of that year on an experimental basis in order to satisfy the demand of passengers visiting Lisbon during Expo '98.

Later in 1998, Cabo Ruivo (on 18 July) and Olivais (on 8 August) opened as infill stations on the Red Line, between Chelas and Oriente.

On 2 November 2002, under Manuel Frasquilho's tenure as president, the Green Line's extension from Campo Grande to Telheiras opened.

[7] Further modernization works to the Lisbon Metro began on 19 July 2017, when the Arroios station on the Green Line was closed for extensive renovations and the expansion of the platforms to allow six-car trains; the station was originally scheduled to reopen in 2019, but reopening was later postponed to no earlier than 2021 due to construction delays.

[10] On 8 May 2017, the government of Portugal announced an extension of the Yellow Line to Cais do Sodré as part of a new operational master plan.

[15][16] An extension to the Red Line is also projected to be built, extending it to four entirely new stations: Campolide/Amoreiras, Campo de Ourique, Infante Santo and Alcântara.

It will connect the area of Infantado, in Loures to the metro station of Odivelas and then to Beatriz Ângelo Hospital, with the line making a "C" shape.

1988: Sete Rios (now Jardim Zoológico) – Colégio Militar/Luz 1997: Colégio Militar/Luz – Pontinha 1998: Restauradores - Baixa-Chiado (Blue and Green Lines split) 2004: Pontinha – Amadora Este 2007: Baixa-Chiado – Santa Apolónia 1988: Entre Campos – Cidade Universitária 1993: Cidade Universitária – Campo Grande 1997: Rotunda (now Marquês de Pombal) – Rato 1966: Rossio - Anjos 1972: Anjos - Alvalade 1993: Alvalade – Campo Grande 1998: Rossio – Cais do Sodré(Blue and Green lines split) 2009: Alameda (II) – São Sebastião (II)

Unlike most metro systems, the trains do not have any form of air conditioning due to the small size of the tunnels.

In 2021, Stadler Rail and Siemens Mobility won a contract to supply 14 three-car trains for Lisbon Metro.

The first train was delivered from the Stadler Rail Valencia SAU factory in Spain on 9 August 2024 and is planned to enter service in January 2025.

[23] In October 2024, Lisbon Metro again signed a contract with Stadler, this time for the supply of 24 three-car trains with an option for 12 more, designated as the ML24 series.

[24] The architecture and decor of an underground station is a key element for the well-being of passengers, and art works to make travel more appealing.

In 1988, with the completion of new expansions, there was still a concern about organizing and decorating stations, thus these stations featured works by contemporary Portuguese artists: Rolando de Sá Nogueira in Laranjeiras, Júlio Pomar in Alto dos Moinhos, Manuel Cargaleiro in Colégio Militar/Luz, and Vieira da Silva in Cidade Universitária.

Since then, art has become the norm in the Lisbon Metro; lighting plays with the brightness of the azulejo tiles that are present in almost every station.

In recent years, the oldest stations have been refurbished, not only to enhance the decor and aesthetics, but also to improve accessibility for passengers with reduced mobility.

Parque station is generally considered to be the most valuable and interesting of them all, where the tiles map details of the Portuguese voyages of discovery and their philosophical and literary links.