The Seoul Metropolitan Subway (Korean: 수도권 전철) is a metropolitan railway system consisting of 23 rapid transit, light metro, commuter rail and people mover lines located in northwest South Korea.

The system serves most of the Seoul Metropolitan Area including the Incheon metropolis and satellite cities in Gyeonggi province.

[4] Most of the system is operated by three companies – Seoul Metro, Korail (Korea Railroad Corporation), and Incheon Metro – with the rest being operated by an assortment of local municipal corporations and private rail companies.

[5] The first section of subway was built using the cheaper cut and cover construction method.

These safety doors were completed by 2017, however many stations previously had metal barriers installed decades beforehand.

[10] The world's first virtual mart for smartphone users opened at Seolleung station in 2011.

All directional signs in the system are written in Korean using Hangul, as well as English and Katakana/Chinese characters for Japanese and Mandarin Chinese.

In the trains, there are in addition many LCD screens giving service announcements, upcoming stop names, YTN news, stock prices and animated shorts.

There are also prerecorded voice announcements that give the upcoming station, any possible line transfer, and the exiting side in Korean, followed by English.

[13] Most trains have digital TV screens, and all of them have air conditioning and climate controlled seats installed that are automatically heated in the winter.

[12] All lines use the T-money smart payment system using RFID and NFC technology for automatic payment by T-money smart cards, smartphones, or credit cards and one can transfer to any of the other line within the system for free.

In 2004 the fare system reverted to charging by distance, and free bus transfers were introduced.

[18] On May 24, 2022, the Sillim Line opened, becoming the newest addition to the Seoul Metropolitan Subway.

Currently, the fare system is distance-based and accepted payment methods are single-use tickets, transportation cards including T-money and Cash Bee.

Transportation cards can also be used on buses, taxis, convenience stores and many other popular retail places.

The current single-use ticket is a credit card-sized plastic card with RFID technology, which can be obtained from automated machines in every subway station.

A 500 won deposit fee is included in the price, and is refunded when the ticket is returned at any station.

Depending on where you purchase the card, the service is limited to the Seoul metropolitan area or Jeju Island and does not work in taxis or certain convenience stores.

[34][35] The following lines have not started construction, but are considered to be approved after their plans and their financing have been finalized.

The Seoul Metropolitan government published a ten-year plan for expansion of the subway with the following projects under consideration.