Although the existential movement in France has had almost a popular success, it is much more than passing fashion in ideas. It has over a century of history behind it, and is already entitled to rank as one of those movements of revolt against over-systematization in philosophy which have occurred from time to time in the course of Western thought, with corrective or stimulating effect. And although existentialism is often described as anti-historical, and in a sense it is, its advocates show no lack of interest in their historical antecedents. The present translation of a lecture by Jean-Paul Sartre, followed by a discussion, may therefore be usefully prefaced by a brief account of the school of thought which it represents.