Group of 3 players (usually 2 vn. and vc., or vn., va., vc.) or comp. written for them to perf. Trios for 2 vn. and vc. were derived from baroque trio sonata. Haydn seems to have been the first to write for vn., va., and vc. and was emulated by Boccherini. Mozart's Divertimento (K563) is a notable example and there are others by Beethoven. An unusual combination of instr. is Dvořák's Terzetto for 2 vn. and va. (1887). In the 20th cent. trios for vn., va., and vc. have been written by Webern (1927), Schoenberg (1945), Dohnányi, Hindemith, Roussel, Moeran, and L. Berkeley. In 1938 Vaughan Williams wrote a double str. trio (2 vn., 2 va., 2 vc.), revised it in 1942, and rewrote it 1946–8 as Partita for str.