Japan (Japanese: 日本, Nippon or Nihon, and formally 日本国, Nihonkoku) is an island country in East Asia. It is situated in the northwest Pacific Ocean and is bordered on the west by the Sea of Japan, extending from the Sea of Okhotsk in the north toward the East China Sea, Philippine Sea, and Taiwan in the south. Japan is a part of the Ring of Fire, and spans an archipelago of 14,125 islands, with the five main islands being Hokkaido, Honshu (the "mainland"), Shikoku, Kyushu, and Okinawa. Tokyo is the nation's capital and largest city, followed by Yokohama, Osaka, Nagoya, Sapporo, Fukuoka, Kobe, and Kyoto.

Japan is the eleventh most populous country in the world, as well as one of the most densely populated and urbanized. About three-fourths of the country's terrain is mountainous, concentrating its population of almost 125 million on narrow coastal plains. Japan is divided into 47 administrative prefectures and eight traditional regions. The Greater Tokyo Area is the most populous metropolitan area in the world.

Japan has been inhabited since the Upper Paleolithic period (30,000 BC). Between the 4th and 9th centuries, the kingdoms of Japan became unified under an emperor and the imperial court based in Heian-kyō. Beginning in the 12th century, political power was held by a series of military dictators (shōgun) and feudal lords (daimyō) and enforced by a class of warrior nobility (samurai). After a century-long period of civil war, the country was reunified in 1603 under the Tokugawa shogunate, which enacted an isolationist foreign policy. In 1854, a United States fleet forced Japan to open trade to the West, which led to the end of the shogunate and the restoration of imperial power in 1868. In the Meiji period, the Empire of Japan adopted a Western-modeled constitution and pursued a program of industrialization and modernization. Amidst a rise in militarism and overseas colonization, Japan invaded China in 1937 and entered World War II as an Axis power in 1941. After suffering defeat in the Pacific War and two atomic bombings, Japan surrendered in 1945 and came under a seven-year Allied occupation, during which it adopted a new constitution.

Under the 1947 constitution, Japan has maintained a unitary parliamentary constitutional monarchy with a bicameral legislature, the National Diet. Japan is a developed country and a great power. It is a member of numerous international organizations, including the United Nations, G20, OECD, and the Group of Seven. Its economy is the world's third-largest by nominal GDP and the fourth-largest by PPP, with its per capita income ranking at 36th highest in the world. Although Japan has renounced its right to declare war, the country maintains Self-Defense Forces that rank as one of the world's strongest militaries. Japan has the world's highest life expectancy, though it is experiencing a population decline. A global leader in the automotive, robotics and electronics industries, the country has made significant contributions to science and technology. Japan is also considered a cultural superpower as the culture of Japan is well known around the world, including its art, cuisine, film, music, and popular culture, which encompasses prominent manga, anime and video game industries.