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.