The legislative assembly of Great Britain has roots dating back to the Middle Ages (500–1350) when a great council, known as the Curia Regis, advised the king. This body was made up of nobility and clergy. The body evolved over time and progressively gained more power to govern.

Today Parliament consists of the House of Commons, a democratically elected body (roughly equivalent to the U.S. House of Representatives); the House of Lords, which consists of noblemen (dukes, marquesses, earls, viscounts, and barons) as well as highranking Anglican clergy (bishops and abbots); and the monarch (king or queen). Since 1911 the power of the House of Lords has been negligible, with the House of Commons charged with electing the prime minister (who must be a member of Commons). The prime minister—not the monarch—is the executive head of government.