A constitution is a set of rules for government—often codified as a written document—that enumerates the powers and functions of a political entity. In the case of countries, this term refers specifically to a national constitution defining the fundamental political principles, and establishing the structure, procedures, powers and duties, of a government. By limiting the government's own reach, most constitutions guarantee certain rights to the people. The term constitution can be applied to any overall law that defines the functioning of a government, including several historical constitutions that existed before the development of modern national constitutions.
Constitutions concern different kinds of political organizations. They are found extensively in regional government, at supranational (e.g., European Union), federal (e.g., Indian Constitution), state or provincial (e.g., the constitution of the Commonwealth of Massachusetts or the constitution of the State of New York), and sub-national levels. They are also found in many political groups, such as political parties, pressure groups, and trade unions.
Non-political entities such as corporations and voluntary associations, whether incorporated or not, may also have a constitution. The constitution of a legally incorporated entity is more usually styled as its memorandum and articles of association (U.S. incorporation).