The House of Councillors is the upper house of the National Diet of Japan. The House of Representatives is the lower house. The House of Councillors is the successor to the pre-war House of Peers. If the two houses disagree on matters of the budget, treaties, or the nomination of the prime minister, the House of Representatives can insist on its decision. In other decisions, the House of Representatives can override a vote of the House of Councillors only by a two-thirds majority of members present.

The National Diet is the national legislature of Japan. It is composed of a lower house, called the House of Representatives, and an upper house, the House of Councillors. Both houses are directly elected under a parallel voting system. In addition to passing laws, the Diet is formally responsible for nominating the Prime Minister. The Diet was first established as the Imperial Diet in 1890 under the Meiji Constitution, and took its current form in 1947 upon the adoption of the post-war constitution. Both houses meet in the National Diet Building in Nagatachō, Chiyoda, Tokyo.