bicameral system (bīkăm´ərəl), governmental system dividing the legislative function between two chambers, an "upper," such as the U.S. Senate and the British House of Lords, and a "lower," such as the U.S. House of Representatives and the British House of Commons. Where bicameral legislatures exist, the two chambers are based on different principles of representation in addition to possessing separate functions. Although the term bicameral was coined by Jeremy Bentham as recently as 1832, division of the legislative branch of government according to function and composition is of long standing.

The division of the English Parliament into separate houses of Lords and Commons in the 14th cent. may have arisen simply for the sake of convenience in transacting business; however, this division came to represent the historic cleavage of interest between nobles and commoners, with the balance of power, especially after the Glorious Revolution of 1688 and the gradual development of cabinet government in the 18th cent., shifting more and more to the commoners. The powers of the House of Lords were drastically reduced by the Parliament acts of 1911 and 1949, and though the house continues to debate and vote on bills, its function has become essentially advisory.

The British colonies in North America gradually adopted the bicameral system; the upper chamber, whether elective or appointive, came to represent the colony as a whole, while delegates to the lower house were attached to particular constituencies. According to modern scholars, the adoption of the same system for the Congress of the United States reflected colonial practice, British example, and the widespread differences in property qualification for suffrage and office-holding purposes current at the time. In France some 18th-century theorists, such as Montesquieu, favored a bicameral legislature based on the British example, but the "natural rights" philosophers, such as Rousseau, opposed such a system. France experimented with various forms of legislature during the Revolutionary and Napoleonic periods but thereafter, despite numerous constitutional changes, retained a bicameral system. After World War I the unicameral legislative system made headway in Eastern Europe, Latin America, and parts of the British dominions. The only U.S. state to have a unicameral legislature is Nebraska, which adopted it in 1934.

See D. Schaffter, The Bicameral System in Practice (1929); J. A. Corry, Elements of Democratic Government (4th ed. rev. 1964); S. H. Beer, Patterns of Government (3d ed. 1973).