A constitution is a system for governance, often coified as a written document, that establishes the rules and principles of an autonomous 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. Most national constitutions also guarantee certain rights to the people. Historically, before the evolution of modern-style, codified national constitutions, the term constitution could be applied to any important law that governed the functioning of a government.