L'Existentialisme est un Humanisme. [Existentialism and Humanism].

Based on a lecture by the same name he gave at Club Maintenant in Paris in October of 1945, Existentialism Is a Humanism remains "a popular starting-point in discussions of existentialist thought" (Mary Warnock). In it, Sartre asserts that the key defining concept of existentialism is that the existence of a person is prior to their essence. The term "existence precedes essence" subsequently became a maxim of the existentialist movement. Put simply, this means that there is nothing to dictate that person's character, goals in life, and so on; that only the individual can define their essence. According to Sartre, "man first of all exists, encounters himself, surges up in the world – and defines himself afterwards".