The United Kingdom of Great Britain is a constitutional monarchy located off the northwestern coast of continental Europe. It is an island country or a spanning cluster of islands including Great Britain, the northeastern part of Ireland, and many small islands. The UK is surrounded by the Atlantic Ocean, the North Sea, the English Channel and the Irish Sea. The largest island, Great Britain, is linked to France by the Channel Tunnel.

The United Kingdom is a unitary state consisting of four countries: England, Northern Ireland, Scotland and Wales. It is governed by a parliamentary system with its seat of government in London, the capital, but with three devolved national administrations in Belfast, Cardiff and Edinburgh, the capitals of Northern Ireland, Wales and Scotland respectively. The head of state of the United Kingdom is Queen Elizabeth II, who has reigned as monarch since 1952. The UK has fourteen overseas territories,  all remnants of the British Empire, which at its height in 1922 encompassed almost a quarter of the world's land surface, the largest empire in history.

The UK is a developed country, with the fifth (nominal GDP) or sixth (PPP) largest economy in the world. It was the world's first industrialised country and the world's foremost power during the 19th and early 20th centuries,  but the economic cost of two world wars and the decline of its empire in the latter half of the 20th century diminished its leading role in global affairs. The UK nevertheless remains a major power with strong economic, cultural, military and political influence. It is a nuclear power and has the second or third highest defence spending in the world. It is a Member State of the European Union, holds a permanent seat on the United Nations Security Council, and is a member of the G8, NATO, OECD, World Trade Organization and the Commonwealth of Nations.