This classic study of the ethics of Jena-Paul Sartre, written in 1947, remains one of the best introductions to Sartre's philosophy and to French existentialism, as it developed in the post-World War II era. It is the only commentary on his thought that Sartre himself ever fully recommended. Jeanson focuses on the doctrine of existentialist morality, which he believes to be inherent, although not articulated, in the works of Sartre. He presents a perspective explication of the relationship between freedom, action, and morality in Sartre's major writings, particularly Being and Nothingness.