Tokyo, officially the Tokyo Metropolis, is the capital and most populous city in Japan. With a population of over 14 million in the city proper in 2023, it is one of the most populous urban areas in the world. The Greater Tokyo Area, which includes Tokyo and parts of six neighboring prefectures, is the most populous metropolitan area in the world, with 41 million residents as of 2024.

Lying at the head of Tokyo Bay, Tokyo is part of the Kantō region, on the central coast of Honshu, Japan's largest island. It is Japan's economic center and the seat of the Japanese government and the Emperor of Japan. The Tokyo Metropolitan Government administers Tokyo's central 23 special wards, which formerly made up Tokyo City; various commuter towns and suburbs in its western area; and two outlying island chains, the Tokyo Islands. Although most of the world recognizes Tokyo as a city, since 1943 its governing structure has been more akin to that of a prefecture, with an accompanying Governor and Assembly taking precedence over the smaller municipal governments that make up the metropolis. Special wards in Tokyo include Chiyoda, the site of the National Diet Building and the Tokyo Imperial Palace; Shinjuku, the city's administrative center; and Shibuya, a hub of commerce and business.

Before the 17th century, Tokyo, then known as Edo, was mainly a fishing village. It gained political prominence in 1603 when it became the seat of the Tokugawa shogunate. By the mid-18th century, Edo was among the world's largest cities, with over a million residents. After the Meiji Restoration (1868), the imperial capital in Kyoto was moved to Edo, and the city was renamed Tokyo (lit. 'Eastern Capital'). Tokyo was greatly damaged by the 1923 Great Kantō earthquake and by allied bombing raids during World War II. From the late 1940s, Tokyo underwent rapid reconstruction and expansion, which fueled the Japanese economic miracle, in which Japan's economy became the second-largest in the world at the time, behind that of the United States. As of 2023, Tokyo is home to 29 of the world's 500 largest companies, as listed in the annual Fortune Global 500—the second highest number of any city.

Tokyo was the first city in Asia to host the Summer Olympics and Paralympics, in 1964 and then in 2021. It also hosted three G7 summits, in 1979, 1986, and 1993. Tokyo is an international hub of research and development and an academic center, with several major universities, including the University of Tokyo, the top-ranking university in Japan. Tokyo Station is the central hub for the Shinkansen, the country's high-speed railway network; and the city's Shinjuku Station is the world's busiest train station. Tokyo Skytree is the world's tallest tower. The Tokyo Metro Ginza Line, which opened in 1927, is the oldest underground metro line in Asia.

Tokyo's nominal gross domestic output was 113.7 trillion yen (US$1.04 trillion) in FY2021 and accounted for 20.7% of Japan's economic output, which converts to 8.07 million yen or US$73,820 per capita. Including the Greater Tokyo Area, Tokyo is the second-largest metropolitan economy in the world after New York, with a 2022 gross metropolitan product estimated at US$2.08 trillion. Although Tokyo's status as a leading global financial hub has diminished with the Lost Decades since the 1990s, when the Tokyo Stock Exchange (TSE) was the world's largest, with a market capitalization about 1.5 times that of the NYSE, Tokyo is still a leading financial hub, and the TSE remains among the world's top five major stock exchanges. Tokyo is categorized as an Alpha+ city by the Globalization and World Cities Research Network. It ranked 14th in the 2024 edition of the Global Livability Ranking, and has been ranked as the safest city in the world in multiple international surveys.