--> ドアが閉まります。ご注意ください。 (''[[http://youtu.be/LWApTBep6no?t=2m43s Doa ga shimarimasu. Gochuui kudasai.]]'')[[note]]"The door is closing. Please be careful."[[/note]]

With how crowded Japan's cities are, it's no surprise that in UsefulNotes/{{Tokyo}} the trains are vital to getting around. Tokyo's rail network is the most extensive of any metropolitan area in the world: on a given day, about 20 million passengers use the network's more than 1,000 stations in [[UsefulNotes/TheFortySevenPrefectures Tokyo, Saitama, Chiba, and Kanagawa Prefectures]] to get from here to there. Shinjuku Station is registered by Guinness as the busiest train station in the entire world at 3.64 million passengers a day. With all that, the actual subways of Tokyo don't make up that big of a percentage of the use - of those 1000+ stations only 290 of them are actually subway stations. Still, an estimated 8.7 million people use them each day, the highest of any city in the world.

But wait - why is it then that a list of the world's busiest metro systems doesn't have Tokyo first (currently Beijing) nor second (Seoul) nor third (Shanghai) [[OverlyLongGag nor fourth]] ([[UsefulNotes/MoscowMetro Moscow]])? Well, there are actually two different subway systems in Tokyo, run by two different administrations. While the two systems cooperate with one another in several areas (most notably the unified system of labeling lines and stations), the separate administrations also mean any trip using both systems incurs a surcharge via a special transfer ticket - a similar situation exists if you wanted to transfer to a line run by JR East, including the Yamanote Line (a new card system called PASMO was introduced in 2007 that simplified the process).

Each line is marked by both a unique color and a symbol containing a circle with that color, with a Latin alphabet letter corresponding to the first letter of that line's Romanized name (generally - in cases of overlap or other potential confusion another letter is used) - the two systems' lines don't repeat either between each other. Each station, in turn, is given a designation of that line's letter followed by what number stop it is along the line for ease of use by foreigners. For example, G-01 is the first station on the Ginza Line (Shibuya), G-02 is the second station on the line (Omotesandō), G-03 is the third (Gaiemmae), and so on. Multiple designations can apply to the same station - Omotesandō is also the fourth station on the Chiyoda Line (C-04) and the second on the Hanzōmon Line (Z-02).

Heavy rail JR and private lines in Tokyo have [[UsefulNotes/TokyoTrainLines their own page.]]

!!Tokyo Metro
The more extensive and used of the two systems. This was formerly the Teito Rapid Transit Authority (or Eidan), run by the Ministry of Land, Infrastructure, and Transport before being privatized in 2004 (albeit co-owned by the Japanese government and the Tokyo Metropolitan government). The company also runs several commercial developments near several of their stations.

* '''C'''hiyoda Line (green, Line 9)
* Han'''Z'''ōmon Line (purple, Line 11)
* '''F'''ukutoshin Line (brown, Line 13)
** The deepest subway line in Japan, with an average depth of 27 meters.
** It was designed to connect Shinjuku, Shibuya and Ikebukuro, something only the Yamanote Line did at the time. The idea was to relieve pressure and overcrowding on the Yamanote.
** Planned in 1972, the first segment (known as the "Yurakucho New Line") didn't open until December 1994, paralleling the Yurakucho Line between Ikebukuro and Kotake-mukaihara in Nerima-ku. The line didn't begin full service for 13 1/2 years, opening on 14 June 2008.
* '''H'''ibiya Line (silver, Line 2)
* '''G'''inza Line (orange, Line 3)
** Known as the "first underground railway in the Orient", the Tokyo Underground Railway was the dream of a businessman who was inspired by the London Underground. The first portion opened in 1927 between Ueno and Asakusa. It was extended to Kanda in 1931, but the Great Depression and expensive wars waged by Showa Japan slowed development. It reached its planned terminus of Shimbashi in 1934.
** At the same time, a company that has ties to today's Tokyu Electric Railway (the Tokyo Rapid Railway) built a subway line between Shibuya and Toranomon, which opened in 1938, and was extended to 1938 to connect to the Tokyo Underground Railway in Shibuya. Through service began a year later, and the two operating companies were merged by the Showa government into the Teito Rapid Transit Authority (or TRTA, known as "Eidan" to locals) in 1941.
** The name "Ginza Line" was coined in 1953, in preparation for the opening of the Marunouchi Line in 1954.
** As Japan's first subway line, the Ginza Line is very shallow, with an average depth of 10 to 12 meters. As a result, trains are very short, only 6-cars, and through service with other rail lines is not possible.
* '''M'''arunouchi Line (red, Line 4)
** Also contains a branch line, designated with a lower case "m".
** Opened in 1954, this U-shaped line is the only subway line to serve Tokyo Station. It connects Ikebukuro with Ochanomizu, Otemachi, Tokyo Station, Ginza, Kasumigaseki (home to most government ministries), Akasaka, Yotsuya, Shinjuku, and the thickly populated residential areas of Nakano and Ogikubo (in Suginami-ku).
** It's also a shallow line, with the same physical restrictions of the Ginza Line (6-cars, no through service). Congestion on the Ginza and Marunouchi Lines were so extreme that TRTA constructed the Hanzomon Line as a parallel relief line.
* '''N'''amboku Line (emerald/dark aqua/teal, Line 7)
* '''T'''ōzai Line (sky blue, Line 5)
** According to Tokyo Metro the Tozai Line has the most crowded portion in the system, running at 199% overcapacity during rush hour between Monzen-Nakacho and Kiba. The encompassing portion between Kasai and Nihonbashi is hellishly overcrowded in its own right.
* '''Y'''ūrakuchō Line (yellow, Line 8)

!!Toei Subway
The smaller of the two systems, run directly by the Tokyo Metropolitan government. Toei also runs several light rail lines, bus lines, and even a fiber optic network and several power generators.

* '''A'''sakusa Line (rose, Line 1)
* M'''I'''ta Line (blue, Line 6)
* Ō'''E'''do Line (magenta or ruby, Line 12)
** If the complexity and headache of having two separate subway systems requiring separate fares in the same city annoys you, blame this - Toei incurred a ton of debt constructing this entirely-underground line in TheNineties (the second-longest rail tunnel in Japan after the Seikan Tunnel connecting Honshu and Hokkaido across the Tsugaru Strait) and Tokyo Metro is reluctant to assume this debt in any deals for the two systems to come under one administration.
* '''S'''hinjuku Line (leaf green, Line 10)

!!Other Major Lines (not part of either system, but still frequently used)
* Yamanote Line - operated by JR East. Runs in a loop that circles around the 23 special wards, frequently marked on both Tokyo Metro and Toei Subway station maps.
* Rinkai Line - underground line run by a non-profit organization near Tokyo's waterfront, connects from Osaki to the waterfront islands of Odaiba.
* Yurikamome Line - Another public transit line that runs to Odaiba. Unlike the Rinkai Line, it is technically a trolleybus[[note]]It runs on rubber tires in a guiding concrete trough, instead of rails[[/note]] rather than a rail system, runs above-ground, and is driverless. Tickets are more expensive, but the ride offers scenic views of the city including a 270-degree loop before it crosses Rainbow Bridge.
* Saitama Rapid Railway - a suburban commuter line that is underground nearly the entire length.

!! Tokyo subways in media
* ''Film/JiroDreamsOfSushi'' opens with titular chef Jiro's daily commute via subway to his restaurant. There's good reason for this: the restaurant is just outside the fare gates at Ginza station.
* ''VideoGame/TheSecretWorld'' opens in a Tokyo subway station where a supernatural disaster has taken place. A couple of stations are also seem later in the game, when the player actually goes to Tokyo.