Simone de Beauvoir (1908–86) was Sartre's lifelong partner, but she was obviously far more than simply that. Not only was she a philosopher of great ability (at the time, she was the youngest ever student to pass the agrégation at the École Normale Superieure and hence be qualified to teach the subject), but she is also a philosopher of enduring significance. According to some sources, The Second Sex (1949) is one of the best-selling non-fiction books published in the twentieth century, and it has been enormously influential on generations of feminists. Moreover, like Sartre, she wrote many novels and fought against oppression in many of its various guises, most notably against imperialism, racism and sexism. Her philosophical project was almost always couched in terms of existentialism and, more particularly, in terms of Sartrean existentialism. The philosophical vernacular of existentialism is all there in her work (for-itself and in-itself, transcendence and immanence, etc.), and she thought of her work as extending Sartre's, or supplementing his, rather than as directly challenging it. However, she in fact poses many challenges to Sartrean existentialism. In different ways she challenges his account of love, oppression, otherness, bad faith and death, and her early and enduring interest in Marxism foreshadowed Sartre's own eventual modifications to his philosophy of freedom, which he presented in his later work Critique of Dialectical Reason. The two main texts by de Beauvoir that we will consider in this chapter are The Second Sex and The Ethics of Ambiguity.