who's who

American  

noun

1. a reference work containing short biographical entries on the outstanding persons in a country, industry, profession, etc..

   a who's who in automotive engineering.

2. the outstanding or influential persons in a community, industry, profession, or other group.

   The who's who of racing will be there.

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who's who British  

noun

1. a book or list containing the names and short biographies of famous people

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who's who Idioms  

1. The outstanding or best-known individuals of a group, as in Tonight's concert features a veritable who's who of musicians. This expression comes from the name of a famous reference work, Who's Who, first published in 1849, which contains biographical sketches of famous individuals and is regularly updated. Its name in turn was based on who is who, that is, the identity of each of a number of persons, a phrase dating from the late 1300s. [Early 1900s]

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Etymology

Origin of who's who

First recorded in 1840–50

Example Sentences

See Examples For:

who's who

“So how does the system know who’s who? And when it flags someone — is it a human decision or just an algorithm flipping a switch?”

From Los Angeles Times ● May 4, 2026

About 120 guests sardined into the modest backyard of Sonenshein’s Santa Monica childhood home, with a veritable who’s who of the L.A. restaurant scene doing double duty as attendees and vendors.

From Los Angeles Times ● Apr. 28, 2026

The dinner brings together journalists and the who's who of Washington to raise funds for scholarships and awards.

From Barron's ● Apr. 26, 2026

Dunkin’ and endorser Ben Affleck, meanwhile, generated more engagement than any other celebrity spot by casting its “Good Will Hunting” parody with a who’s who of hit ’90s sitcoms including “Friends,” “Seinfeld” and “Family Matters.”

From The Wall Street Journal ● Feb. 9, 2026

I only know who’s who because each of us is labeled.

From "Zara’s Rules for Record-Breaking Fun" by Hena Khan