The primary component of a legislature is 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 may 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. For this purpose the upper house may either contain the delegates of state governments, as is the case of Germany and was the case in the pre-20th century United States, or be elected according to a formula that grants disproportionate representation to smaller states, as is the case today in Australia and the United States.