The United Kingdom of Great Britain and Northern Ireland (usually shortened to the United Kingdom or the UK) is a country located off the north-western coast of continental Europe, surrounded by the North Sea, the English Channel, the Celtic Sea, the Irish Sea, and the Atlantic Ocean.

The Palace of Westminster, on the banks
of the River Thames

It is composed of four constituent parts: three constituent countries—England, Scotland, and Wales—on the island of Great Britain, and the province of Northern Ireland on the island of Ireland. The border between Northern Ireland and the Republic of Ireland forms the United Kingdom's principal international land border, although there is a nominal frontier with France in the middle of the Channel Tunnel.

The UK has several overseas territories and the Crown dependencies of the Isle of Man and the Channel Islands come under the UK's sovereignty. The UK also has close relationships with the fifteen other Commonwealth Realms, as they all share the same head of state. The UK is also one of the largest member states of the European Union and a founding partner of both the UN and NATO.