The British Empire was the largest empire in history and for a time was the foremost global power. It was a product of the European age of discovery, which began with the maritime explorations of the 15th century, that sparked the era of the European colonial empires. By 1921, the British Empire held sway over a population of about 458 million people, approximately one-quarter of the world's population. It covered about 36.6 million km² (14.2 million square miles), about a quarter of Earth's total land area. As a result, its legacy is widespread, in legal and governmental systems, economic practice, militarily, educational systems, sports, and in the global spread of the English language. At the peak of its power, it was often said that "the sun never sets on the British Empire" because its span across the globe ensured that the sun was always shining on at least one of its numerous colonies or subject nations.

During the five decades following World War II, most of the territories of the Empire became independent. Many went on to join the Commonwealth of Nations, a free association of independent states.