Adachi (足立区, Adachi-ku^?) is one of the special wards of Tokyo, Japan. It is located north of the heart of Tokyo. The ward consists of two separate areas: a small strip of land between the Sumida River and Arakawa River and a larger area north of the Arakawa River. The ward is bordered by the cities of Kawaguchi, Sōka and Yashio in Saitama and Katsushika, Sumida, Arakawa, and Kita in Tokyo.

The ward is called Adachi City in English.

Adachi has sister-city relationships with Belmont, Australia. Within Japan, Adachi has similar ties with the city of Uonuma (formerly the town of Koide) in Niigata Prefecture, Yamanouchi in Nagano Prefecture, and the city of Kanuma in Tochigi Prefecture.

As of April 1, 2011, the ward has an estimated population of 645,365, with 305,264 households, and a population density of 12,130.92 persons per km². The total area is 53.20 km².

The Adachi Land Transportation Office is located here, and automobiles registered at this office bear Adachi number plates.

Under the Ritsuryō system, the present-day ward was the southern extremity of Adachi District, Musashi Province. In 826, during the Heian period, the Nishiarai Daishi temple was founded. During the Muromachi period and into the Sengoku period, the Chiba clan held control of the region. The Great Senju Bridge was built in 1594. In the Edo period, parts were under the direct control of the Tokugawa shogunate, and parts were under the administration of Kan'ei-ji, a temple in present-day Ueno, Tokyo. Adachi was also home to Senju-shuku was a post station on both the Nikkō Kaidō and the Mito Kaidō. The shogunate maintained the Kozukappara execution grounds in Senju. In 1932, Adachi became a ward of Tokyo City. The special ward was founded on March 15, 1947.

Tokyo (東京, Tōkyō^?, "Eastern Capital") [toːkʲoː], English /ˈtoʊki.oʊ/; officially Tokyo Metropolis (東京都, Tōkyō-to^?), is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of the world. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family. Tokyo is in the Kantō region on the southeastern side of the main island Honshu and includes the Izu Islands and Ogasawara Islands. Tokyo Metropolis was formed in 1943 from the merger of the former Tokyo Prefecture (東京府, Tōkyō-fu^?) and the city of Tokyo (東京市, Tōkyō-shi^?).

The Tokyo Metropolitan government administers the 23 special wards of Tokyo (each governed as a city), which cover the area that was the city of Tokyo, as well as 39 municipalities in the western part of the prefecture and the two outlying island chains. The population of the special wards is over 8 million people, with the total population of the prefecture exceeding 13 million. The prefecture is part of the world's most populous metropolitan area with upwards of 35 million people and the world's largest urban agglomeration economy with a GDP of US$1.479 trillion at purchasing power parity in 2008, ahead of New York City metropolitan area, which ranks second on the list. The city hosts 47 of the Fortune Global 500 companies, the highest amount of any city.

Masao Adachi (足立正生 Adachi Masao, born May 13, 1939 in Fukuoka Prefecture) is a Japanese screenwriter and director who was most active in the 1960s and 1970s.

Best known for his writing collaborations with directors Kōji Wakamatsu and Nagisa Oshima, often under the pseudonyms "Izuru Deguchi" or "De Deguchi" (出口出), he also directed a number of his own films, usually dealing with left-wing political themes. He stopped making films in the early 1970s and joined the Japanese Red Army, an armed militant organization. After residing in Lebanon for 28 years, he was arrested for passport violations. He was found guilty of passport violations in September 2001 and received a four-year sentence, suspended to 18 months. After his release he was deported to Japan via Jordan, where he was re-arrested on other passport violations. After being held for a year and a half he was convicted and released based on the time he had already served. Since his release, he has resumed making films after a 30 year absence.