Under the constitution of England as it has existed for several centuries, Parliament, the legislative department of the government of Great Britain, is composed of two houses, and their concurrence in legislation is necessary. The membership of the upper house consists of lords, both secular and ecclesiastical, whose titles are derived from the crown, and the lower branch, or House of Commons, is composed of members chosen by a limited suffrage. In the colonial governments there was usually provision for some sort of legislative assembly of two branches, the members of the upper branch being appointed by the king or his representative, the governor, and the members of the lower branch elected by the people. It was natural, therefore, that in the earliest state constitutions, as well as in the federal constitution, it should be provided that the legislative power should be vested in an assembly consisting of two branches, the higher branch less numerous than the lower, and that the concurrence of the two branches should be essential to the enactment of laws. This so-called bicameral system is found also in other countries, and possesses some theoretical and practical advantages which have been sufficient to cause it to be retained in the formation of the later state constitutions. Indeed, this system is so fully recognized and firmly established that it may be regarded as a part of our plan of republican government.

In England the assent of the king to legislation proposed by Parliament has always been regarded as essential, and it was natural that the approval of the chief executive should likewise be required in the state and federal constitutions. But in England the king is not a part or component element of Parliament, and it cannot be properly said that the delegation of the veto power to the executive renders the executive a branch of the legislative department in the matter of legislation. The functions of the executive in approving or vetoing proposed legislation will therefore properly be discussed in one of the chapters relating to the executive power. (See below, ch. xxi.) Although in Great Britain and also in the colonial governments the higher branch of the legislative body was composed of appointed members, the higher branch, under our system of government, usually called the Senate, as well as the lower and more numerous branch, usually called the House of Representatives, is composed of members selected by some form of election; but the qualifications and method of election of the members of the higher branch may be somewhat different from those provided in case of members of the lower branch. This is especially noticeable with reference to the organization of Congress, the senators being regarded as representatives of the states, while the members of the House of Representatives are selected by vote of the people in separate districts of each state.