In this chapter, I will address two questions: What was Sartre's contribution to psychology and to what extent was Sartre's psychology influenced by Heidegger's thought? I will concentrate on Sartre's existential psychoanalysis as outlined in Being and Nothingness (Sartre, 1956). After some preliminaries, I give an account of Sartre's existential psychoanalysis and then, in the third section of the chapter, review the intellectual encounter between Heidegger and Sartre, especially as it bears on the early Sartre's alternative to the several incarnations of empirical psychoanalysis, which began with Freud.