Who's Who (or "Who is Who") is the title of a number of reference publications, generally containing concise biographical information on a particular group of people. The title is also used as an expression meaning a collection or group of noted persons; as in the sentence, "The actors in the film were a Who's Who of the great American comedians of the time".
The title "Who's Who" is in the public domain, and thousands of Who's Who compilations of varying scope and quality have been published by various authors and publishers. The oldest and best known is the annual British publication Who's Who, a reference work on contemporary prominent people. Another reputable and long standing publication is Canadian Who's Who, which has published biographies of prominent Canadians based on merit alone since 1910.
However, many publications using the title are vanity publications, where the inclusion criterion is the biographee's willingness to buy the book, with the business model consisting of selling books directly to the biographees.
Who's Who in American Real Estate, a resource tool of professional real estate agents in America since 1983.
Who's Who of Southern Africa, a resource tool of noteworthy people in Southern Africa, and a professional networking platform. It is not the same as the official print publication, but a website which anyone may join and create their own profile.
Hinterland Who's Who, a series of 60-second public service ads profiling Canadian animals and birds, produced by Environment Canada in the 1960s