Who's Who (or "Who is Who") is the title of a number of reference publications, generally containing concise biographical information on the prominent people of a country. The title has been adopted as an expression meaning a group of notable persons.
The oldest and best-known is the annual publication Who's Who, a reference work on contemporary prominent people in Britain published annually since 1849.
The title "Who's Who" is in the public domain, and thousands of Who's Who compilations of varying scope and quality (and similar publications without the words "Who's Who") have been published by various authors and publishers. Many such publications can be described as Who's Who scams; they list any people likely to buy the book, or to pay for inclusion, with no criterion of genuine notability. In some cases the publisher also sells its list of biographees, optionally broken down by profession, sex, political affiliation or religion, to direct mail marketers.
Some Who's Who books have a title in the language of the country concerned: