The United Kingdom of Great Britain and Northern Ireland (usually shortened to the United Kingdom, the UK, or Britain) is a country and sovereign state that is situated to the north west of mainland Europe. Its territory and population are primarily situated on the island of Great Britain and in Northern Ireland on the island of Ireland. The United Kingdom is bounded by the Atlantic Ocean, and its ancillary bodies of water, including the North Sea, the English Channel, the Celtic Sea, and the Irish Sea. The mainland is linked to France by the Channel Tunnel, with Northern Ireland sharing a land border with the Republic of Ireland.
The United Kingdom is a political union made up of four constituent countries: England, Scotland, Wales and Northern Ireland. The United Kingdom also has several overseas territories, including Bermuda, Gibraltar, Montserrat and Saint Helena among others. The dependencies of the Channel Islands and the Isle of Man, formally possessions of the Crown, form a federacy with the United Kingdom collectively known as the British Islands. A constitutional monarchy, the United Kingdom is a Commonwealth Realm, sharing the same person — Queen Elizabeth II — with the fifteen other Realms as monarch and head of state, forming a personal union with each.