Tracing her intellectual development from her university years, when she was trained in a Cartesian and neo-Kantian philosophical tradition, to her final decade, during which she was recognised as having inspired the emerging strands of late twentieth-century feminism, Beauvoir is shown to have been among the most influential philosophical voices of the mid twentieth century. Countering the recent trend to read her in isolation from Sartre, she is shown to have both adopted, adapted, and influenced his philosophy, most importantly through encouraging him to engage with Hegel and to consider our relations with others. The Second Sex is read in the light of her existentialist humanism and ultimately faulted for having succumbed too uncritically to the masculine myth that it is men who are solely responsible for society’s intellectual and cultural history.