"Ad Lib" was one of three duets choreographed by Merce Cunningham and Jean Erdman for a joint concert of work by Cunningham, Erdman and Nina Fonaroff. According to Erdman, this duet was "in the jazz idiom," with a structure determined in collaboration with John Cage. As the title indicates, the movement was at least partly improvised. The duet was originally danced with music by Gregory Tucker; a later production used John Cage’s composition "Ad Lib".