L'Être et le Néant
"Being and Nothingness" is regarded as both the most important non-fiction expression of Sartre's existentialism and his most influential philosophical work, original despite its debt to Heidegger. Many have praised the book's central notion that "existence precedes essence", its introduction of the concept of bad faith, and its exploration of "nothingness", as well as its novel contributions to the philosophy of sex. However, the book has been criticized for its abstruseness and for its treatment of Freud.