The British Empire comprised the dominions, colonies, protectorates, mandates, and other territories ruled or administered by the United Kingdom and its predecessor states. It began with the overseas possessions and trading posts established by England in the late 16th and early 17th centuries. At its height in the 19th and early 20th century, it was the largest empire in history and, for a century, was the foremost global power. By 1913, the British Empire held sway over 412 million people, 23 percent of the world population at the time, and by 1920, it covered 35.5 million km2 (13.7 million sq mi), 24 per cent of the Earth's total land area. As a result, its constitutional, legal, linguistic, and cultural legacy is widespread. At the peak of its power, it was described as "the empire on which the sun never sets", as the sun was always shining on at least one of its territories.

A dominion was any of several largely self-governing countries of the British Empire. Progressing from colonies, their degrees of colonial self-governance increased unevenly over the late 19th century through the 1930s, and some vestiges of empire lasted in some areas into the late 20th century. With the evolution of the British Empire into the Commonwealth of Nations, finalised in 1949, the dominions became independent states, either as Commonwealth republics or Commonwealth realms.