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.

---

who's who British  

noun

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

---

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]

---

Etymology

Origin of who's who

First recorded in 1840–50

Example Sentences

See Examples For:

who's who

But the list of female journalists he’s gone after in anger reads like a who’s who of the Washington press corps writ large.

From Slate ● Aug. 18, 2026

The donors are a who’s who of tech leaders, venture capitalists and other leaders in the gig, gaming, digital media and AI defense fields.

From Los Angeles Times ● May 18, 2026

His putting allowed him to fend off a who’s who of stars, shooting a five-under in the final round at a course that had driven players mad all week.

From The Wall Street Journal ● May 17, 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