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

In the comments section of Skylight’s post announcing the big news, the who’s who of L.A.’s literati popped the proverbial champagne.

From Los Angeles Times ● Apr. 16, 2026

Kelly: We've also had a fair few people talk about being at your 40th birthday in January and it was like a who's who of football...

From BBC ● Mar. 21, 2026

"He knows my players, he's well aware of who's who, and some of them still can't get their head around that when I tell them."

From Barron's ● Feb. 25, 2026

“How do you know who’s who if they don’t smell?”

From "The One and Only Ivan" by Katherine Applegate