In addition to tone clusters evident in such works as Advertisement and Tiger, Cowell experimented with the "string piano" in works like The Aeolian Harp and The Banshee where strings are strummed or plucked inside the piano. Studies of the musical cultures of Africa, Java, and North and South India enabled Cowell to stretch and redefine Western notions of melody and rhythm; mastery of the gamelan and the theory of gamelan composition led to further explorations with exotic instruments and percussion. Later, Cowell developed the concept of indeterminancy or "elastic form" in works like the Mosaic Quartet (where performers determine the order and alternation of movements).
Cowell's influence is legion, counting among his students John Cage, Lou Harrison, and George Gershwin. Cowell taught at the New School for Social Research in New York and also held posts at the Peabody Conservatory and Columbia University. A plethora of awards, grants, and honorary degrees was capped by his election in 1951 to the American Institute of Arts and Letters.