In this paper I attempt to further the case, made in recent years by Eva Gothlin, that readers interested in a philosophical return to Simone de Beauvoir's The Second Sex have good reason to heed Beauvoir's appropriation of central concepts from Heidegger's Being and Time. I speculate about why readers have been hesitant to acknowledge Heidegger's influence on Beauvoir and show that her infrequent though, I argue, important use of the Heideggarian neologism Mitsein in The Second Sex makes inadequate sense apart from an appreciation of the fundamental role played by her appropriation of Hegel's "master-slave dialectic" in that book. I suggest a way to square Beauvoir's Hegelian claim that human beings are fundamentally at odds with one another with her Heideggerian view that we are also all ontologically "with" one another. Finally, I sketch out a way of interpreting Beauvoir's employment of certain concepts from Hegel and Heidegger in the service of understanding, hence beginning to overcome, women's oppression.