Who's Who in the Theatre is a British reference work, first published in 1912 with sixteen new editions from then until its last issue in 1981.
The book was a successor to The Green Room Book, of which four editions were published between 1906 and 1909. Both works presented brief biographies of well-known members of the theatrical profession, listing all the productions they had appeared in, written, produced or been associated with. Who's Who in the Theatre aimed from the outset to cover Broadway theatre as well as that of the West End and, to a lesser extent, the British provinces.
The editor from 1912 to 1952 was John Parker, a successful businessman, who in addition to his commercial activities was a well-known theatre critic. He was succeeded for a single edition by his son, and then from 1961 to 1968 by Freda Gaye, a former actress and first curator of the British Theatre Museum, and finally by Ian Herbert who was in charge of the last three editions.
As well as the theatrical biographies, the contents varied from edition to edition, but generally included details of major West End productions since the previous edition, lists of long-running productions in London and New York, plans and details of London theatres, and for many years family trees of leading theatrical dynasties.