Many nations around the world use a parliamentary system, with different forms and institutions that shape the way they function. These systems differ, but most are based on the idea of the legislature being the supreme legislative body in the country. Legislators in parliamentary systems derive their democratic legitimacy from the support and “confidence” of a majority of legislators, to whom they are held accountable. This is in contrast to presidential systems, where the head of government derives their democratic legitimacy from the support of a minority of voters and is not fully accountable to the legislature.
Different parliamentary systems have different methods of selecting members, but most involve public elections in which citizens vote for a political party or individual to represent them in the legislature. There are also differences in the electoral system, such as whether or not it uses proportional representation and the rules for the distribution of seats among parties.
The Westminster model, common in the Commonwealth and countries influenced by British political tradition, tends to have a more adversarial style of debating and places greater importance on committees than on plenary sessions. These parliaments are usually unicameral, and they sometimes use a form of proportional representation with open party lists.
Some parliamentary systems have a constitutional court that can declare laws unconstitutional, and in some there are special legislative procedures such as the requirement for a two-thirds supermajority to pass legislation. Generally, however, the people collectively possess the only check on an otherwise supreme legislature, by voting legislators and their party out of office in the next election.