In a bicameral Westminster System parliament, the House of Commons has traditionally been the name of the elected lower house. The Commons generally holds much more power than the upper house (the Senate or House of Lords). The leader of the majority party in the House of Commons usually becomes the prime minister. The existing Houses of Commons are:

The House of Commons was also the lower house in Parliament of Ireland, before its abolition under the 1801 Act of Union , and the short-lived Parliament of Southern Ireland in 1920, which was subsequently renamed Dáil Éireann. Similarly, House of Commons was the lower house of the Parliament of Northern Ireland, before its abolition in 1972.

In other bicameral systems, the lower house may be known by one of the following names: