A legislature is a governmental deliberative body with the power to adopt laws. Legislatures are known by many names including parliament, general assembly, senate, or congress. In parliamentary systems of government, the legislature is formally supreme and appoints the executive. In presidential systems of government, the legislature is considered a branch of government which is equal to the executive.

The power of legislatures vary widely from country to country. A rubber stamp legislature is a derogative name used for a legislature that has no real power and simply approves bills which are put before it.

Legislatures can be roughly divided into two groups: unicameral legislatures and bicameral legislatures. The latter are composed of two separate divisions or houses (bi two, camera chamber) with different duties, powers, and methods for selection of members. Examples of bicameral legislatures include the British Parliament (divided into the House of Lords and the House of Commons) and the United States Congress (divided into the Senate and the House of Representatives). Generally both houses must agree on important legislation for it to be enacted. Examples of unicameral legislatures include those of the Canadian provinces and territories.

That branch of government whose function is to enact laws. Under the United States Constitution, this power is given to Congress. The powers of Congress are limited to those contained in Article I, Section 8 of the Constitution. Among these powers are the power to tax, the power to regulate interstate and foreign commerce, and the power to declare war, among others.

The legislative branch of government in the United States is limited by the separation of powers among the other branches of government. For example, the Executive branch headed by the President of the United States has the power veto legislation. The Judicial branch also maintains a check on the power of the legislature called judicial review, in which legislation is examined to ensure its compatibility with the Constitution. Legislation found to be incompatible is struck down.

Compare this system of checks and balances with the system in the United Kingdom. There, the executive is the British monarch, who is essentially a figurehead whose power is restricted by convention and public opinion. The Prime Minister, generally regarded as being the real authority in the UK, is himself or herself a member of Parliament, which is the legislature.

See also: List of legislatures.