The United Kingdom is a country made up of four countries (England, Wales, Scotland, and Northern Ireland) that are joined together and share the same government. The document that explains and sets out how this government works is called the Constitution. It explains who has the power in the government and how they can use it. It also explains how laws are made and changed, how people can get involved in how the country is run and how the government is held accountable. All the countries in the United Kingdom have agreed to abide by the Constitution, which means they all need to agree on any changes that are being made.