He was a political radical all his life and a passionate enthusiast for such diverse things as medieval music, The Jungle Book of Rudyard Kipling, Johann Sebastian Bach, film stars (especially Lilian Harvey and Ginger Rogers), traveling, stereoscopic photography and socialism.
His mother's family came from Alsace and he identified with that region; his maternal grandfather had been the noted philanthropist and textile manufacturer Jean Dollfus, and Koechlin inherited his strongly developed social conscience.
His fellow students included George Enescu, Ernest Le Grand, Reynaldo Hahn, Max d'Ollone, Henri Rabaud and Florent Schmitt.
In 1909 he began regular work as a critic for the Chronique des Arts and in 1910 was one of the founders, with Ravel, of the Société musicale indépendante, with whose activities he was intensely associated.
At first comfortably off, he divided his time between Paris and country homes in Villers-sur-Mer and the Côte d'Azur, but after the onset of World War I his circumstances were gradually reduced; he had to sell one of his houses and in 1915 began working as a lecturer and teacher.
Partly because of his constant advocacy of younger composers and new styles, he was never successful in his attempts to gain a permanent teaching position for himself, though he was an examiner for many institutions (e.g. the Conservatoires of Brussels, Rheims and Marseilles).
[2] On the 1929 visit his symphonic poem La Joie païenne won the Hollywood Bowl Prize for Composition and was performed there under the baton of Eugene Goossens.
In the 1940s, however, the music department of Belgian Radio took up his cause and broadcast several premieres of important scores including the first complete performance of the Jungle Book cycle.
He was highly eclectic in inspiration (nature, the mysterious orient, French folksong, Bachian chorale, Hellenistic culture, astronomy, Hollywood movies, etc.)
After World War I his continuing devotion to the symphonic poem and the large orchestra at a period when neoclassicism and small ensembles were more fashionable may have discouraged performance and acceptance of his works.
His compositions include the four symphonic poems and three orchestral songs making up Livre de la jungle after Rudyard Kipling; many other symphonic poems including Le Buisson Ardent after Romain Rolland (this is a diptych of two orchestral poems, performable separately) and Le Docteur Fabricius after a novel by his uncle Charles Dollfus; three string quartets; five symphonies including a Seven Stars Symphony inspired by Hollywood; sonatas for flute, oboe, clarinet, bassoon, horn, violin, viola and cello, and much other chamber music; many songs, over two hundred opus numbers in all; and a vast number of monodies, fugal studies, chorale harmonizations and other educational pieces.
The twelve tone technique is one of the several modern music styles parodied in the 'Jungle Book' symphonic poem Les Bandar-Log, but Koechlin also wrote a few pieces in what he described as the 'style atonal-sériel'.
His Seven Stars Symphony features movements inspired by Douglas Fairbanks, Lilian Harvey, Greta Garbo, Clara Bow, Marlene Dietrich, Emil Jannings and Charlie Chaplin in some of their most famous film roles.
In addition to the Fauré Pelléas et Mélisande (suite mentioned above), he orchestrated the bulk of Claude Debussy's 'legende dansée' Khamma under the composer's direction, from the piano score [1] Archived 31 August 2006 at the Wayback Machine, and orchestrated Cole Porter's ballet Within the Quota; other works he transcribed include Schubert's Wanderer Fantasy and Chabrier's Bourrée fantasque.