Abstract: The research subject is the types of musical action art - instrumental theatre, director’s action art, instrumental multimedia. The research object is the works of several third stream composers of the late 20th - the early 21st century which contain the distinctive features of musical action art. Based on the typology formulated by the researcher V.O.Petrov, the author studies the issues connected with the synthesis of music, text, theatrical elements and multimedia. Special attention is given to the instrumental theatre genre. The research field contains: the synthetic opus by the third stream theorist G. Schuller ‘Journey into Jazz’; an orchestra cycle by a modern Brooklyn band leader D.Argue ‘Real Enemies’; an orchestra play ‘W.A.Mozart VS Random Generator’ from the creative project Live on Planet Earth by Brooklyn composer and a leader of a big band Andromeda Mega Express Orchestra D. Glatzel; a double concert R.A.P. by Schuller’s follower and junior colleague in New England Conservatory in Boston, American composer T. McKinley. The author analyzes their works and detects the signs of the synthesis of music, text, visual multimedia action and particular theatrical elements. In all the works under study the esthetic principles of the instrumental theatre genre can be identified, which prove its importance and topicality during the development of the musical art of the late 20th - the early 21st century.