The Hong Kong handover, domestically known as the transfer of sovereignty over Hong Kong, was the formal passing of authority over the territory of the then colony of Hong Kong from the United Kingdom to the People's Republic of China at midnight on 1 July 1997. This event ended 156 years of British rule in the former colony. Hong Kong was established as a special administrative region of China (SAR) for 50 years, maintaining its own economic and governing systems from those of mainland China during this time, although influence from the central government in Beijing increased after the passing of the Hong Kong national security law in 2020.Hong Kong had been a colony of the British Empire since 1841, except for four years of Japanese occupation from 1941 to 1945. After the First Opium War, its territory was expanded on two occasions; in 1860 with the addition of Kowloon Peninsula and Stonecutters Island, and again in 1898, when Britain obtained a 99-year lease for the New Territories. The date of the handover in 1997 marked the end of this lease. The 1984 Sino-British Joint Declaration had set the conditions under which Hong Kong was to be transferred, with China agreeing to maintain existing structures of government and economy under a principle of "one country, two systems" for a period of 50 years. Hong Kong became China's first special administrative region; it was followed by Macau after its transfer from Portugal in 1999 under similar arrangements.

With a 1997 population of about 6.5 million, Hong Kong constituted 97 percent of the total population of all British Dependent Territories at the time and was one of the United Kingdom's last significant colonial territories. Its handover marked the end of British colonial prestige in the Asia-Pacific region where it had never recovered from the Second World War, which included events such as the sinking of Prince of Wales and Repulse and the Fall of Singapore, as well as the subsequent Suez Crisis after the war. The transfer, which was marked by a handover ceremony attended by Charles, Prince of Wales (now King Charles III) and broadcast around the world, is often considered to mark the definitive end of the British Empire.

The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a sovereign country in north-western Europe, 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 within the British Isles. Northern Ireland shares a land border with the Republic of Ireland. Otherwise, the United Kingdom is surrounded by the Atlantic Ocean, with the North Sea to the east, the English Channel to the south and the Celtic Sea to the south-west, giving it the 12th-longest coastline in the world. The Irish Sea separates Great Britain and Ireland. The total area of the United Kingdom is 93,628 square miles (242,500 km2), with an estimated population in 2020 of over 67 million.The United Kingdom is a unitary parliamentary democracy and constitutional monarchy. The monarch, Queen Elizabeth II, has reigned since 1952. The capital and largest city is London, a global city and financial centre with a metropolitan area population of 14 million. Other major cities include Birmingham, Manchester, Glasgow, Liverpool and Leeds.

The United Kingdom consists of four countries: England, Scotland, Wales and Northern Ireland. Other than England, the constituent countries have their own devolved governments, each with varying powers.The United Kingdom has evolved from a series of annexations, unions and separations of constituent countries over several hundred years. The Treaty of Union between the Kingdom of England (which included Wales, annexed in 1542) and the Kingdom of Scotland in 1707 formed the Kingdom of Great Britain. Its union in 1801 with the Kingdom of Ireland created the United Kingdom of Great Britain and Ireland. Most of Ireland seceded from the UK in 1922, leaving the present United Kingdom of Great Britain and Northern Ireland, which formally adopted that name in 1927.The nearby Isle of Man, Guernsey and Jersey are not part of the UK, being Crown Dependencies with the British Government responsible for defence and international representation. There are also 14 British Overseas Territories, the last remnants of the British Empire which, at its height in the 1920s, encompassed almost a quarter of the world's landmass and a third of the world's population, and was the largest empire in history. British influence can be observed in the language, culture and the legal and political systems of many of its former colonies.The United Kingdom has the world's fifth-largest economy by nominal gross domestic product (GDP), and the tenth-largest by purchasing power parity (PPP). It has a high-income economy and a very high human development index rating, ranking 13th in the world. The UK became the world's first industrialised country and was the world's foremost power during the 19th and early 20th centuries. Today the UK remains one of the world's great powers, with considerable economic, cultural, military, scientific, technological and political influence internationally. It is a recognised nuclear state and is ranked fourth globally in military expenditure. It has been a permanent member of the United Nations Security Council since its first session in 1946.

The United Kingdom is a member of the Commonwealth of Nations, the Council of Europe, the G7, the Group of Ten, the G20, the United Nations, NATO, AUKUS, the Organisation for Economic Co-operation and Development (OECD), Interpol, and the World Trade Organization (WTO). It was a member state of the European Communities (EC) and its successor, the European Union (EU), from its accession in 1973 until its withdrawal in 2020 following a referendum held in 2016.