Tehran, the capital of Iran, started construction of a metro system already during the reign of the Shah, but due to financing problems the first mass transit line could not open until March 1999. This was the suburban line (shown on maps as Line 5) which links Tehran to the satellite town of Mehrshahr, some 40 km west of Tehran. Meanwhile construction of the first two metro lines also had advanced and the first stretch of Line 2, which links the Tehran terminus of the Mehrshahr Line to the city centre at Imam Khomeini, started regular service in February 2000. Since then, the network has been gradually expanded by adding more urban lines:

At Imam-Khomeini-Square, the east-west Line 2 intersects with Line 1, which runs north-south. A first 10 km section opened in August 2001. The second stage from Darvazeh Dowlat to Mirdamad (7 km, 8 stations) opened in March 2002 and another 5 km stretch was added in Oct 2002. This line was then extended towards the south to Imam's Holy Shrine, with intermediate stations opening in stages. The former branch from Shahed to Shahr-e Aftab was extended in 2017 to the airport; the 31 km Airport express shuttle was initially referred to as "Line 8", but is now shown as part of Line 1; this branch is to be extended west to Parand (approx. 18 km).

28-08-2001: Ali Abad - Darvazeh Dowlat (10 km)
18-03-2002: Darvazeh Dowlat - Mirdamad (7 km)
23-10-2002: Ali Abad - Shahr-e-Rey (5 km)
xx-03-2003: Shahr-e-Rey - Haram-e-Motahar (Imam's Holy Shrine) (except intermediate stations)
31-05-2009: Mirdamad - Gholhak
31-01-2010: Gholhak - Gheitarieh (excluding intermediate station)
31-07-2010: Shahid Sadr station
21-07-2011: Haram-e-Motahar - Kahrizak
19-02-2012: Gheitarieh - Tajrish
18-04-2016: Shahed - Shahr-e Aftab (4 km)
07-08-2017: Shahr-e Aftab - Imam Khomini International Airport IKIA (26.2 km)

Renamed stations:
Khazaneh > (2016) Shahid Bokharaei; Baghershahr > (2017) Palayeshgah; Shahed > (2017) Shahed - Baghershahr

At present, Line 2 is 22 km long and has 22 stations. Eleven 7-car trains (137 m long) serve the line at a 2-minute headway, with 3rd-rail power supply (750V).

21-02-2000: Tehran (Sadeghieh) - Imam Khomeini (9 stations - 9.3 km)
17-03-2004: Imam Khomeini - Baharestan (1.6 km, 2 stations)
17-03-2006: Baharestan - Elm-o-Sanat University (not all intermediate stations, only Shahid Madani and Sarsabz)
01-07-2006: Darvazeh Shemiran and Sabalan stations
15-02-2009: Elm-o-Sanat University - Tehran Pars
10-06-2010: Tehran Pars - Farhangsara

Renamed stations:
Nezam Abad > (~2006) Fadak; Azadi > (2015) Shademan

Line 3 runs 37 km from the southwest to the northeast. Construction started in mid-2007, the first section has been operational since Dec 2012. In September 2015 it reached Ghaem, with several intermediate stations being completed at a later date.

16-12-2012: Vali-e Asr* - Shahid Beheshti (7 km, without intermediate stations)
22-04-2014: Vali-e Asr* - Azadegan (with intermediate stations Moniriyeh, Rahahan, Javadiyeh & Ghal'e Morghi*)
02-03-2015: Meydan-e Vali-e Asr + Shahrak-e Shariati stations
17-05-2015: Shahid Doctor Fatemi station
30-06-2015: Abdoladab station
22-09-2015: Shahid Beheshti - Ghaem (with only Zeyn-o-ddin and Nobonyad opening as intermediate stations)
09-11-2015: Ne'mat Abad station
10-02-2016: Mirzaye Shirazi station
06-06-2016: Khajeh Abdollah-e Ansari station
08-08-2016: Sohrevardi station
14-09-2016: Shahid Ghoddoosi station
07-11-2016: Shahid Sayyad-e Shirazi station
12-12-2016: Hossein Abad station
04-02-2017: Heravi station
17-06-2017: Shahid Mahallati station
15-05-2021: Aghdasieh station

Renamed stations:
Ghal'e Morghi > (2014) Zam Zam;
*Vali-e Asr > (2016) Teatr-e Shahr

22 km; east-west line, first section opened in 2008. Airport branch operated separately with 3-car trains.

19-04-2008: Ferdowsi - Darvazeh Shemiran (2.5 km)
16-03-2009: Darvazeh Shemiran - Shohada Square
31-05-2009: Ferdowsi - Enghelab Square (excluding intermediate station)
11-10-2010: Shohada Square - Shahid Kolahdooz (5.5 km) (without intermediate stations)
11-12-2010: Vali-e-Asr* and Nabard stations
07-02-2011: Enghelab Square - Meydan-e Azadi (with only Towhid station in between)
09-05-2011: Doctor Habib-o-Ilah station
27-08-2011: Sheykh-o-raeis* station
05-11-2011: Ostad Moein station
09-01-2012: Piroozi station
16-06-2012: Niroo Havaei station
23-07-2012: Meydan-e Azadi - Ekbatan (without Bimeh)
15-03-2016: Bimeh station + Mehr Abad Airport branch (2 km)
01-05-2023: Eram-e Sabz - Allameh Ja'fari (1.4 km)

*Renamed stations:
Ekbatan - Eram-e Sabz > (2014) Eram-e Sabz; Vali-e Asr > (2016) Teatr-e Shahr; Sheykh-o-raeis > (2016) Ebn-e Sina;

The Tehran-Karaj-Mehrshahr Express Line is a 66 km commuter surface line, which uses 6 double-deck 8-car-trains (248 m), locomotive-drawn with catenary (25KV), 10-minutes headway, 12 stations.

07-03-1999: Tehran - Karaj (3 stations - 31.5 km)
14-03-2005: Iran Khodro station
15-03-2005: Karaj - Golshahr (9 km)
01-06-2005: Chitgar station
13-11-2006: Atmosfer station
18-09-2007: Ekbatan station added
10-10-2010: Mohammad Shahr (now Mahdasht) station
18-02-2017: Garmdarreh station
31-12-2019: Golshahr - Hashtgerd (25.7 km)

07 Apr 2019: Shohada Square - Dowlat Abad (9 km) feat. 1 intermediate station: Besat
28 Sept 2019: Shohada Square - Emam Hossein (1 km)
17 Feb 2020: Kian Shahr station
17 Dec 2020: Amir Kabir station
13 Mar 2021: Yadegar-e Emam - Shahid Sattari (isolated operation)
16 Mar 2021: Yadegar-e Emam - Tarbiat Modarres University and Shahid Ashrafi Esfahani station
15 May 2021: Marzdaran station
17 Jun 2021: Shahrak-e Azmayesh station
11 Oct 2021: Shahid Rezaei station
18 Mar 2023: Tarbiat Modares University – Emam Hossein (9.5 km)

Eventually running from Yousef Abad in the north to Takhti Stadium in the southeast, becoming 31 km long with 34 stations:

10 June 2017: Meydan-e San'at - Basij (22 km - 7 stations) (official premature inauguration!)
21 Sept 2017: Tarbiat Modarres University station
25 Sept 2017: Roudaki station
14 July 2018: Stations reopened after the line had been closed for several months: Navab Safavi - Roudaki - Komeyl - Beryanak and Mahdieh.
16 Mar 2019: Meydan-e San'at, Tarbiat Modarres University and Helal Ahmar stations (re)opened
19 Aug 2019: Mohammadieh Square and Basij stations (re)opened
23 Dec 2019: Molavi station added
16 Nov 2020: Tehran Milad Tower station added
04 Mar 2021: Ghiam Square (Meydan-e Ghiyam) and Doolab stations added
16 Mar 2021: Ahang station
17 Jun 2021: Modafean-e Salamat station
22 Dec 2021: Towhid station
16 Mar 2022: Goftogo Park station
11 June2022: 17th Shahrivar station
18 Mar 2023: Meydan-e San'at – Shahid Dadman (1.5 km)

Renamed stations:
Doolab > (2021) Chehel Tan-e Doolab; Bagher Khan > (2021) Modafean-e Salamat

Photos © Toma Bacic

Line 2 may later be extended further east to connect with a suburban line to Damavand and Pardis.

Four more lines are on the drawing board (see map)

Tehran Metro (official page)

Tehran Metro Story (doc, 15MB, from official site)

Tehran Metro Group

Non-offical Iran Railways Page (includes some subway info)

Tehran Metro at Wikipedia