The United Kingdom of Great Britain and Northern Ireland[note 7] (commonly known as the United Kingdom, the UK, or Britain) is a sovereign state[7][8] located off the northwestern coast of continental Europe. It is an island nation,[9] spanning an archipelago including Great Britain, the northeastern part of the island of Ireland, and many smaller islands. Northern Ireland is the only part of the UK with a land border[note 8] with another sovereign state, sharing it with the Republic of Ireland.[10][11] Apart from this land border, the UK is surrounded by the Atlantic Ocean, the North Sea, the English Channel and the Irish Sea.

The United Kingdom is a constitutional monarchy and unitary state. It is a country[12][13] consisting of four countries: England, Northern Ireland, Scotland and Wales.[14] It is governed by a parliamentary system with its seat of government in the capital city of London. There are three devolved national administrations of varying powers[15][16] in Belfast, Cardiff and Edinburgh, the capitals of Northern Ireland, Wales and Scotland respectively. The UK has three Crown Dependencies [17] and fourteen overseas territories that are not constitutionally part of the UK.[18] These territories are 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. As a result, British influence can still be observed in the language, culture and legal systems of many of its former colonies.

The UK is a developed country, with the world's sixth largest economy by nominal GDP and the sixth largest by purchasing power parity. It was the world's first industrialised country[19] and the world's foremost power during the 19th and early 20th centuries,[20] but the economic and social 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 great power with