The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) and colloquially Great Britain (GB) or simply Britain, is a sovereign country in western Europe. Lying off the north-western coast of the European mainland, the United Kingdom includes the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands. Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state—the Republic of Ireland. Apart from this land border, the United Kingdom is surrounded by the Atlantic Ocean, with the North Sea to its east, the English Channel to its south and the Celtic Sea to its south-south-west, giving it the 12th-longest coastline in the world. The Irish Sea lies between Great Britain and Ireland.
The United Kingdom is a constitutional monarchy with a parliamentary democracy. The capital of the United Kingdom and its largest city is London, a global city and financial centre with an urban area population of 10.3 million, the fourth-largest in Europe and second-largest in the European Union. The United Kingdom consists of four countries—England, Scotland, Wales and Northern Ireland. The last three have devolved administrations, each with varying powers, based in their capitals, Edinburgh, Cardiff and Belfast, respectively. The nearby Isle of Man, Bailiwick of Guernsey and Bailiwick of Jersey are not part of the United Kingdom, being Crown dependencies with the British Government responsible for defence and international representation.