After women secured the right to vote some hundred years ago, the assertions about their innate inferiority gradually began to vanish, giving way to theories about the countless aspects which apparently differentiated them from men. In this paper, we follow the evolution of research on sex differences, starting with the work of the first female psychologists who questioned the theories that justified women’s subordinate positions in society. We trace the main developments of the studies on sex differences, their relationship with social roles, gender stereotypes, and gender identity, and describe the strategies used to highlight the role of society rather than of biology in shaping men and women’s personalities and behaviors. We describe the controversies this area of research gave rise to, the debates over its political implications, and the changes observed over time in women’s social positions and within research perspectives. Finally, we discuss the mutually reinforcing effects of social organization and lay conceptions of gender and reflect on how the field of research on sex differences has contributed to building a fairer society.