The 16.8 km line serves the wards of Shibuya, Minato, Chiyoda, Chūō, Kōtō, and Sumida. Despite being shorter in length than nearly all other Tokyo subway lines, the Hanzōmon Line operates some of the longest through services with private railways – namely Tōkyū Corporation and Tobu Railway. The line is connected to Tōkyū Den-en-toshi Line at Shibuya Station to the south, and to the Tobu Skytree Line at to the north. Through trains operate between on the Tōkyū Den-en-toshi Line and on the Tobu Skytree Line, onward to on the Tobu Isesaki Line and on the Tobu Nikko Line. Through-service trains between Chūō-Rinkan and Minami-Kurihashi cover a total distance of 98.5 km in a single run – more than five times the length of the Hanzōmon Line alone. The Hanzōmon Line has direct interchanges with all other Tokyo Metro and Toei lines. It connects with the Tokyo Metro Ginza Line at five stations, which in turn is named after 16th century samurai Hattori Hanzō, who was important to the founding of the shogunate which built the palace. The Hanzōmon Line's color on maps and station guides is purple, and stations carry the prefix "Z" followed by a number. According to the Tokyo Metropolitan Bureau of Transportation, as of June 2009 the Hanzōmon Line is the sixth most crowded subway line in Tokyo, at its peak running at 173% capacity between Shibuya and Omotesandō stations.
The Hanzōmon Line was first planned in 1971, along with the Chiyoda Line and Yūrakuchō Line, as a reliever line for the heavily congested Ginza Line. Its initial routing was from Futako-Tamagawa Station on the Tōkyū Den-en-toshi Line to a new station in the Fukagawa district of Kōtō Ward. In 1985, a second draft plan from the Ministry of Transportation moved the Hanzōmon Line's final terminus to Matsudo, Chiba Prefecture. During the planning stage, it was known as Line 11. Construction began in 1972 and the majority of the line was expected to open in 1975. However, the poor economy in Japan had depressed the Teito Rapid Transit Authority's receipts during that time, which considerably delayed the construction of new lines. On August 1, 1978, the first section of the Hanzōmon Line finally opened from Shibuya to Aoyama-itchōme, including through services with the Den-en-toshi Line. It was then extended to Nagatachōin September 1979. However, the next extension posed political problems, as the original plan had the line run directly under the Imperial Palace to Ōtemachi. TRTA decided to divert the route around the north side of the Imperial Palace, which required the construction of three new stations. An eminent domain battle erupted with landowners along the proposed route, which delayed the completion of the next stage of the line. Hanzomon Station opened in December 1982, and the full extension around the Imperial Palace, terminating at Mitsukoshi-mae, was not completed until January 1989. Since then, there have been further extensions to Suitengu-mae and finally Oshiage, the latter also enabling through service with the Tobu Skytree Line. The Ministry of Transportation estimated in 2000 that the line would be extended to Matsudo in 2015. However, Tokyo Metro stated in its initial public offering that its construction operations would cease once the Fukutoshin Line is completed, which casts some doubt as to whether the Matsudo extension will actually be built.
