A legislature is a deliberative assembly with the authority to make laws for a political entity such as a country or city. Legislatures form important parts of most governments; in the separation of powers model, they are often contrasted with the executive and judicial branches of government.
The members of a legislature are called legislators. In a democracy, legislators are most commonly popularly elected, although indirect election and appointment by the executive are also used, particularly for bicameral legislatures featuring an upper chamber.
Each chamber of the legislature consists of a number of legislators who use some form of parliamentary procedure to debate political issues and vote on proposed legislation. There must be a certain number of legislators present to carry out these activities; this is called a quorum.
The members of a legislature usually represent different political parties; the members from each party generally meet as a caucus to organize their internal affairs.
Some political systems follow the principle of legislative supremacy, which holds that the legislature is the supreme branch of government and cannot be bound by other institutions, such as the judicial branch or a written constitution. Such a system renders the legislature more powerful.
A legislature may debate and vote upon bills as a single unit, or it may be composed of multiple separate assemblies, called by various names including legislative chambers, debate chambers, and houses, which debate and vote separately and have distinct powers. A legislature which operates as a single unit is unicameral, one divided into two chambers is bicameral, and one divided into three chambers is tricameral.
In federations, the upper house typically represents the federation's component states. This is a case with the supranational legislature of the European Union. The upper house may either contain the delegates of state governments – as in the European Union and in Germany and, before 1913, in the United States – or be elected according to a formula that grants equal representation to states with smaller populations, as is the case in Australia and the United States since 1913.
Legislature size is a trade off between efficiency and representation; the smaller the legislature, the more efficiently it can operate, but the larger the legislature, the better it can represent the political diversity of its constituents. Comparative analysis of national legislatures has found that size of a country's lower house tends to be proportional to the cube root of its population; that is, the size of the lower house tends to increase along with population, but much more slowly.