The United Kingdom of Great Britain and Northern Ireland (commonly known as the United Kingdom, the UK or Britain) is a sovereign state located off the north-western coast of continental Europe.
The country 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 UK that shares a land border with another sovereign state—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 United Kingdom is a unitary state governed under a constitutional monarchy and a parliamentary system, with its seat of government in the capital city of London.
It is a country in its own right and consists of four countries: England, Northern Ireland, Scotland and Wales.
There are three devolved administrations, each with varying powers, based in Belfast, Edinburgh and Cardiff, the capitals of Northern Ireland, Scotland and Wales respectively.
England with London as its capital is governed directly by the UK government.
Associated with the UK, but not constitutionally part of it, are three Crown Dependencies of Jersey, Guernsey and the Isle of Man.
The United Kingdom has 14 overseas territories.
These are remnants of the British Empire which, at its height in 1922, encompassed almost a quarter of the world's land surface and was the largest empire in history.
British influence can still be observed in the language, culture and legal systems of many of its former territories.
The UK is a developed country.
It was the world's first industrialised country and the world's foremost power during the 19th and early 20th centuries.
The UK remains a great power with leading economic, cultural, military, scientific and political influence.
The UK has been a permanent member of the United Nations Security Council since its first session in 1946.
It has been a member of the European Union and its predecessor the European Economic Community since 1973.
It is also a member of the Commonwealth of Nations, the Council of Europe, the G7, the G8, the G20, NATO, the Organisation for Economic Co-operation and Development (OECD) and the World Trade Organisation.
The UK was originally called the United Kingdom of Great Britain and Ireland but after Southern Ireland became independent in 1931 the current official name was adopted.
England, Wales and Ireland were formerly ruled by the King of England and the King of Scotland was an independent ruler but the ascent of Scottish King James 1 to the throne of England on July 25, 1603 resulted in the formation of a union of equal partners comprising the four countries.
In the Olympics, the UK is titled Great Britain because Northern Ireland's sportspeople are entitled to dual citizenship of the UK and the Republic of Ireland and the option of representing either the UK or Ireland.
The total area of the United Kingdom is approximately 243,610 square kilometres.
The country occupies the major part of the British Isles and includes the island of Great Britain, the north-eastern one-sixth of the island of Ireland and some smaller surrounding islands.
It lies between the North Atlantic Ocean and the North Sea with the south-east coast coming within 35 kilometres of the coast of northern France, from which it is separated by the English Channel.
The United Kingdom lies between latitudes 49° to 61° N, and longitudes 9° W to 2° E.
Northern Ireland shares a 360-kilometre land boundary with the Republic of Ireland.
The coastline of Great Britain is 17,820 kilometres long.
It is connected to continental Europe by the Channel Tunnel, which at 50 kilometres (38 kilometres underwater) is the longest underwater tunnel in the world.
England accounts for just over half of the total area of the UK, covering 130,395 square kilometres.
Most of the country consists of lowland terrain, with mountainous terrain north-west of the Tees-Exe line including the Cumbrian Mountains of the Lake District, the Pennines and limestone hills of the Peak District, Exmoor and Dartmoor.
The main rivers and estuaries are the Thames, Severn and the Humber.
England's highest mountain is Scafell Pike (978 metres) in the Lake District.
Its principal rivers are the Severn, Thames, Humber, Tees, Tyne, Tweed, Avon, Exe and Mersey.
Scotland accounts for just under a third of the total area of the UK, covering 78,772 square kilometres and including nearly eight hundred islands, predominantly west and north of the mainland, notably the Hebrides, Orkney Islands and Shetland Islands.
The topography of Scotland is distinguished by the Highland Boundary Fault — a geological rock fracture — which traverses Scotland from Arran in the west to Stonehaven in the east.
The faultline separates two distinctively different regions namely the Highlands to the north and west and the lowlands to the south and east.
The more rugged Highland region contains the majority of Scotland's mountainous land, including Ben Nevis which at 1,343 metres is the highest point in the British Isles.
Lowland areas, especially the narrow waist of land between the Firth of Clyde and the Firth of Forth known as the Central Belt, are flatter and home to most of the population including Glasgow, Scotland's largest city and Edinburgh, its capital and political centre.
Wales accounts for less than a tenth of the total area of the UK, covering 20,779 square kilometres.
Wales is mostly mountainous, though South Wales is less mountainous than North and Mid Wales.
The main population and industrial areas are in South Wales, consisting of the coastal cities of Cardiff, Swansea and Newport and the South Wales Valleys to their north.
The highest mountains in Wales are in Snowdonia and include Snowdon which at 1,085 metres is the highest peak in Wales.
The 14, or possibly 15, Welsh mountains over 914 m high are known collectively as the Welsh 3000s.
Wales has over 1,200 km of coastline.
There are several islands off the Welsh mainland, the largest of which is Anglesey in the northwest.
Northern Ireland accounts for just 14,160 square kilometres and is mostly hilly.
It includes Lough Neagh which, at 388 square kilometres is the largest lake in the British Isles.
The highest peak in Northern Ireland is Slieve Donard in the Mourne Mountains at 852 metres.
The United Kingdom has a temperate climate, with plentiful rainfall all year round.
The temperature varies with the seasons seldom dropping below −11 °C or rising above 35 °C.
The prevailing wind is from the south-west and bears frequent spells of mild and wet weather from the Atlantic Ocean, although the eastern parts are mostly sheltered from this wind — as the majority of the rain falls over the western regions the eastern parts are therefore the driest.
Atlantic currents, warmed by the Gulf Stream, bring mild winters especially in the west where winters are wet and even more so over high ground.
Summers are warmest in the south-east of England, being closest to the European mainland and coolest in the north.
Heavy snowfall can occur in winter and early spring on high ground and occasionally settles to great depth away from the hills.
The United Kingdom is a unitary state under a constitutional monarchy.
Queen Elizabeth II is the head of state of the UK as well as of 15 other independent Commonwealth countries.
The monarch has "the right to be consulted, the right to encourage, and the right to warn".
The United Kingdom has an uncodified constitution, as do only three other countries in the world.
The Constitution of the United Kingdom thus consists mostly of a collection of disparate written sources, including statutes, judge-made case law and international treaties, together with constitutional conventions.
As there is no technical difference between ordinary statutes and "constitutional law" the UK Parliament can perform "constitutional reform" simply by passing Acts of Parliament and thus has the political power to change or abolish almost any written or unwritten element of the constitution.
However, no Parliament can pass laws that future Parliaments cannot change.
The position of prime minister, the UK's head of government, belongs to the member of parliament who can obtain the confidence of a majority in the House of Commons, usually the current leader of the largest political party in that chamber.
The prime minister and cabinet are formally appointed by the monarch to form Her Majesty's Government, though the prime minister chooses the cabinet and, by convention, the Queen respects the prime minister's choices.
England and Scotland were leading centres of the Scientific Revolution from the 17th century and the United Kingdom led the Industrial Revolution from the 18th century, and has continued to produce scientists and engineers credited with important advances.
Major theorists from the 17th and 18th centuries include Isaac Newton, whose laws of motion and illumination of gravity have been seen as a keystone of modern science, from the 19th century Charles Darwin, whose theory of evolution by natural selection was fundamental to the development of modern biology, and James Clerk Maxwell, who formulated classical electromagnetic theory, and more recently Stephen Hawking, who has advanced major theories in the fields of cosmology, quantum gravity and the investigation of black holes. Wikipedia.