British Americans are citizens of the United States whose ancestry originates wholly or partly in the United Kingdom (England, Wales, Scotland and Northern Ireland). The term is seldom used by people to refer to themselves (1,172,050 chose it in the 2009 American Community Survey) and is used primarily as a demographic or historical research term. In the modern age, it can refer to British people who live and work in the United States (some of whom become American citizens), and Americans who do the same in the United Kingdom.

According to American Community Survey in 2009 data, Americans reporting British ancestry made up an estimated (40,234,652) or 13.0% of the total U.S. population, and form the third largest European ancestry group after German Americans and Irish Americans. This is an approx 35% drop from the population figures derived from the 1980 United States Census.

However, demographers regard this as an undercount as the index of inconsistency is high, and many, if not most, people from English stock have a tendency to identify simply as Americans or, if of mixed European ancestry, nominate a more recent and differentiated ethnic group. Consequently, many well-established white Americans have at least some British ancestry^{[citation needed]}, including many who identify primarily with other ethnic groups (such as Irish, German, Scandinavian, and so forth).

British people (also referred to as the British, Britons, or informally as Brits or Britishers) are citizens or natives of the United Kingdom, of the Isle of Man, of any of the Channel Islands, or of any of the British overseas territories, and their descendants.British nationality law governs modern British citizenship and nationality, which can be acquired, for instance, by birth in the UK or by descent from British nationals. When used in a historical context, the term British people refers to the ancient Britons, the indigenous inhabitants of Great Britain south of the Forth.

Although early assertions of being British date from the Late Middle Ages, the creation of the Kingdom of Great Britain in 1707 triggered a sense of British national identity. The notion of Britishness was forged during the Napoleonic Wars between Britain and the First French Empire, and developed further during the Victorian era. The complex history of the formation of the United Kingdom created a "particular sense of nationhood and belonging" in Great Britain; Britishness became "superimposed on much older identities", of English, Scots and Welsh cultures, whose distinctiveness still resist notions of a homogenised British identity. Because of longstanding ethno-sectarian divisions, British identity in Northern Ireland is controversial, but it is held with strong conviction by unionists.