What is a constitution?

A constitution is a set of principes laid out in a document for the running of a country. It covers the role of the executive (Prime Minister or President), the legislature (e.g. House of Commons) and the judiciary (Supreme Court). Laws that are passed in a country usually have to be within the laws of the constitution, and constitutional law is generally much harder to change than other law, giving it extra protection. In the United States for example, constitutional amendment needs the support of two thirds of both houses of Congress and three quarters of state legislatures. Constitutions also often incorporate a Bill of Rights, which guarantee fundamental human rights.