Influenced by Jules Massenet, Gabriel Fauré, and André Gédalge, under whom he studied, Koechlin experimented with the techniques of polytonality (the use of two or more keys simultaneously) and of atonality and serialism, both of which abandon traditional tonality. Much of his music has a strong flavour of music written in the medieval modes. His writings include treatises on modal polyphony, harmony, and orchestration, and an essay on polytonal and atonal music. His works range from songs, piano works, and chamber music to symphonic and choral works, film music, and ballet. They include songs and symphonic poems on episodes from Rudyard Kipling's Jungle Book (1925–39) and the choral work L'Abbaye (1899–1908).