The National Diet of Japan (国会, Kokkai^?) is Japan's bicameral legislature. It is composed of a lower house, called the House of Representatives, and an upper house, called the House of Councillors. Both houses of the Diet are directly elected under a parallel voting system. In addition to passing laws, the Diet is formally responsible for selecting the Prime Minister. The Diet was first convened as the Imperial Diet in 1889 as a result of adopting the Meiji constitution. The Diet took its current form in 1947 upon the adoption of the postwar constitution and is considered by the Constitution to be the highest organ of state power. The National Diet Building is located in Nagatachō, Chiyoda, Tokyo.

The houses of the diet are elected under a parallel voting system. This means that the seats to be filled in any given election are divided into two groups, each elected by a different method; the main difference between the houses is in the sizes of the two groups and how they are elected. Voters are also asked to cast two votes: one for an individual candidate in a constituency, and one for a party list. Any national of Japan at least twenty years of age (the age of majority in Japan) may vote in these elections. Japan's parallel voting system is not to be confused with the Additional Member System used in many other nations.

Japan ⁱ/dʒəˈpæn/ (Japanese: 日本 Nihon or Nippon; formally 日本国  Nippon-koku or Nihon-koku, literally the State of Japan) is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. The characters that make up Japan's name mean "sun-origin", which is why Japan is sometimes referred to as the "Land of the Rising Sun".

Japan is an archipelago of 6,852 islands. The four largest islands are Honshū, Hokkaidō, Kyūshū and Shikoku, together accounting for ninety-seven percent of Japan's land area. Japan has the world's tenth-largest population, with over 127 million people. The Greater Tokyo Area, which includes the de facto capital city of Tokyo and several surrounding prefectures, is the largest metropolitan area in the world, with over 30 million residents.

Archaeological research indicates that people lived in Japan as early as the Upper Paleolithic period. The first written mention of Japan is in Chinese history texts from the 1st century AD. Influence from other nations followed by long periods of isolation has characterized Japan's history. In the late 19th and early 20th centuries, victory in the First Sino-Japanese War, the Russo-Japanese War and World War I allowed Japan to expand its empire during a period of increasing militarism. The Second Sino-Japanese War of 1937 expanded into part of World War II in 1941, which came to an end in 1945 following the atomic bombings of Hiroshima and Nagasaki. Since adopting its revised constitution in 1947, Japan has maintained a unitary constitutional monarchy with an emperor and an elected parliament called the Diet.