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 in west Northern Europe. Its territory and population are primarily situated on the island of Great Britain and in Northern Ireland on the island of Ireland, with additional settlements on numerous smaller islands in the surrounding seas. 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 and Northern Ireland shares 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 Isle of Man and the Channel Islands, while possessions of the Crown and part of the British Isles, are not part of the United Kingdom. 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.
A member of the G8, the United Kingdom is a highly developed country with the fifth largest economy in the world, estimated at US$1.8 trillion. It is the third most populous state in the European Union with a population of 60.2 million and is a founding member of the North Atlantic Treaty Organisation (NATO) and the United Nations (UN), where it holds a permanent seat on the Security Council. The UK is also one of the world's major nuclear powers.
After the end of the British Empire, the UK retains influence throughout the world because of the extensive use of the English language as well as through the world-spanning Commonwealth of Nations, headed by Queen Elizabeth II.