In recent years the role of religion in the avant-garde has begun to attract scholarly interest. The present volume focuses on the work of the Romanian Jewish poet and visual artist Isidore Isou (1925-2007) who founded the lettrist movement in the 1940s. The Jewish tradition played a critical part in the Western avant-garde as represented by lettrism. The links between lettrism and Judaism are substantial, yet they have been largely unexplored until now. The study investigates the works of a movement that explicitly emphasises its vanguard position while relying on a medieval religious tradition as a source of radical textual techniques. It accounts for lettrism’s renunciation of mainstream traditions in favour of a subversive tradition, in this case Jewish mysticism. The religious inclination of lettrism also affects the notion of the avant-garde. The elements of the Jewish tradition in Isou’s theories and artistic production evoke a broader framework where religion and experimental art supplement each other.