The United Kingdom of Great Britain and Northern Ireland (commonly known as the United Kingdom, the U.K., or Britain) is a country to the northwest of mainland Europe. It comprises the island of Great Britain, the northeast part of the island of Ireland and many small islands. Northern Ireland is the only part of the UK with a land border, sharing it with the Republic of Ireland. Apart from this land border, 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 parliamentary democracy and a constitutional monarchy comprising four constituent countries — England, Northern Ireland, Scotland and Wales — with Elizabeth II as head of state. The Crown Dependencies of the Channel Islands and the Isle of Man, formally possessions of the Crown, are not part of the UK but form a federacy with it. The UK has fourteen overseas territories, all remnants of the British Empire, which at its height encompassed almost a quarter of the world's land surface. As a direct result of the empire, British influence can be observed in the infrastructure, culture, sporting preferences and language of many leading countries all over the globe including Australia, Canada, New Zealand and the United States of America as well as in less globally influential independent states. Queen Elizabeth II remains the head of the Commonwealth of Nations and head of state of the Commonwealth realms. It is a developed country, with the sixth largest economy in the world by PPP and nominal GDP.

Britain was the world's foremost power during the 19th and early 20th century, 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 retains significant economic, cultural, military and political influence and is a nuclear power, with the second highest defence spending in the world. It holds a permanent seat on the United Nations Security Council, and is a member of the G8, NATO, the European Union and the Commonwealth of Nations.

Flag

The United Kingdom of Great Britain and Northern Ireland uses as its national flag the royal banner locally known as the Union Flag or, popularly, Union Jack (although this name is the only one that is correct when the flag is flown on a jackstaff at sea). The current design of the Union Flag dates from the union of Ireland and Great Britain in 1801. It consists of the red cross of Saint George (patron saint of England), edged in white, superimposed on the diagonal red cross of Saint Patrick (patron saint of Ireland), which are superimposed on the Saltire of Saint Andrew (patron saint of Scotland).