A legislature is a type of representative deliberative assembly with the power to create and change laws. The law created by a legislature is called legislation or statutory law. Legislatures are known by many names, the most common being parliament and congress, although these terms also have more specific meanings.

The main job of the legislature is to make and amend laws. In parliamentary systems of government, the legislature is formally supreme and appoints the executive. In presidential systems of government, the legislature is considered a power branch which is equal to and independent of the executive. In addition to enacting laws, legislatures usually have exclusive authority to raise taxes and adopt the budget and other money bills.

The primary components of a legislature are one or more chambers or houses: assemblies that debate and vote upon bills. A legislature with only one house is called unicameral. A bicameral legislature possesses two separate chambers, usually described as an upper house and a lower house, which often differ in duties, powers, and the methods used for the selection of members. Much rarer have been tricameral legislatures; the most recent existed in the waning years of white-minority rule in South Africa.

In most parliamentary systems, the lower house is the more powerful house while the upper house is merely a chamber of advice or review. However, in presidential systems, the powers of the two houses are often similar or equal. In federations it is typical for the upper house to represent the component states; the same applies to the supranational legislature of the European Union. For this purpose the upper house may either contain the delegates of state governments, as is the case in the European Union and in Germany and was the case in the United States before 1913, or be elected according to a formula that grants equal representation to states with smaller populations, as is the case in Australia and the modern United States.

Because members of legislatures usually sit together in a specific room to deliberate, seats in that room may be assigned exclusively to members of the legislature. In parliamentary language, the term seat is sometimes used to mean that someone is a member of a legislature. For example, saying that a legislature has 100 "seats" means that there are 100 members of the legislature, and saying that someone is "contesting a seat" means they are trying to get elected as a member of the legislature. By extension, the term seat is often used in less formal contexts to refer to an electoral district itself, as for example in the phrases "safe seat" and "marginal seat".

See also

• Legislative Assembly
• Legislative Council