British Israelism (also called Anglo-Israelism) is a pseudohistorical belief that the people of Great Britain are "genetically, racially, and linguistically the direct descendants" of the Ten Lost Tribes of ancient Israel. With roots in the 16th century, British Israelism was inspired by several 19th-century English writings such as John Wilson's 1840 Our Israelitish Origin. From the 1870s onward, numerous independent British Israelite organizations were set up throughout the British Empire as well as in the United States; as of the early 21st century, a number of these organizations are still active. In the United States, the idea gave rise to the Christian Identity movement.

The central tenets of British Israelism have been regarded as pseudoscientific and refutable by archaeological, ethnological, genetic, and linguistic research by mainstream sources.

The earliest expressions of the belief that the people of Northern Europe, and especially the British Isles are the direct descendants of the Old Testament Israelites are found in the work of Jacques Abbadie, a French Huguenot theologian. In his 1723 tract, Le Triomphe de la Providence et de la Religion, he argued that the ten lost tribes had migrated north into the Christianised Roman Empire, and that the rise of Protestantism was the fulfilment of Biblical prophecy.

Aspects of British Israelism and its influences have also been traced to Richard Brothers, who published A Revealed Knowledge of the Prophecies and Times in 1794, John Wilson's Our Israelitish Origin (1844), and John Pym Yeatman's The Shemetic Origin of the Nations of Western Europe (1879).

British Israelism arose in England, and then spread to the United States. Its adherents cite various supposedly-medieval manuscripts to claim an older origin, but British Israelism appeared as a distinct movement in the early 1880s:

Although scattered British Israel societies are known to have existed as early as 1872, there was at first no real move to develop an organization beyond the small groups of believers which had arisen spontaneously. The beginnings of the movement as an identifiable religious force can, therefore, be more accurately placed in the 1880s, when the circumstances of the time were particularly propitious for the appearance of a movement so imperialistically-orientated.

The extent to which the British clergy became aware of the existence of the movement may be gauged by the comment which Cardinal John Henry Newman (1801–1890) made when he was asked why he had left the Church of England in 1845 in order to join the Roman Catholic Church. He said that there was a very real danger that the movement "would take over the Church of England."

In the late 19th century, Edward Hine, Edward Wheler Bird, and Herbert Aldersmith developed the British Israelite movement. Hine and Bird achieved a degree of "doctrinal coherence" by eliminating competing forms of the ideology: in 1878, the Anglo-Ephraim Association of London, which followed Wilson by accepting the broader community of western European Germanic peoples as fellow Israelites who were also favoured by God, was absorbed into Bird's Metropolitan Anglo-Israel Association, which espoused the Anglo-exclusive view promoted by Hine.