any of numerous biographical dictionaries that give brief and pertinent information about prominent living persons who are distinguished in a particular field or by official position or public standing and who have, in most cases, supplied data about themselves through publisher questionnaires. Among the most accessible primary sources for biographical information, Who's Who entries may include such personal facts as names of immediate family and salient data about education, business, and military experience; residential and business addresses usually appear. The accuracy of personal information is, however, susceptible to the respondent's whim and is rarely checked.

The first Who's Who was published in London (1849) as a handbook of titled classes, listing only names without biographical sketches. Since 1899 the format has been that of a biographical dictionary, with primarily British emphasis; annual and enlarged publication has continued. Who's Who in America: A Biographical Dictionary of Notable Living Men and Women, first published in Chicago (1899), is issued biennially, thoroughly revised. It is considered the standard, authoritative work of contemporary biography for the United States, and it has included, since 1974, some prominent persons from other countries and representatives to the United Nations. Published as supplements are U.S. regional Who's Whos; Who Was Who, listing deceased persons formerly in Who's Who; and the International Who's Who. In recent decades, national Who's Whos have proliferated in countries throughout the world. Similar biographical dictionaries have emerged focussing on special fields, e.g., natural sciences, banking, government, and politics.