He claimed to have invented the term vers libre, or free verse; he was in any case one of the first European exponents of the form. His principal publications include Les Palais nomades, 1887, Domaine de fée, 1895, and Le Livre d'images, 1897. Kahn also made a valuable contribution to the history of the movement with his book Symbolistes et décadents, 1902.
In addition to his poems, Kahn was a public intellectual who wrote novels, plays, and literary criticism. He played a key role in a number of periodicals, including La Vogue, La Revue Indépendante, La Revue Blanche and Le Mercure de France. He was also an art critic and collector who stayed current with developments in painting and sculpture until his death. He also played a role in a number of debates on public issues, including anarchism, feminism, socialism, and Zionism. In the 1920s he was (head)editor of Menorah, a Jewish bimonthly magazine which folded in 1933.