Although girls and women in many societies avidly participate in sports, they have been traditionally underrepresented compared with boys and men. In this review, we address the apparent sex differences in sports interest and motivation from an evolutionary perspective. First, we demonstrate that females' underrepresentation generally reflects lesser interest, not merely fewer opportunities for engagement. Moreover, there is mounting evidence that male and female athletes generally differ in their motivation, specifically their competitiveness and risk taking. Second, we examine the functional explanations for sports. We argue that the courtship display hypothesis applies mainly to females; the spectator lek hypothesis applies chiefly to males; and that 2 other hypotheses-the allying with coalitions hypothesis and the development of skills hypothesis-are important for both females and males. Third, we explore the proximate causes for the sex differences in sports interest and motivation. We show that although there is compelling evidence that prenatal hormones contribute, the evidence that socialization plays a role remains equivocal. We conclude by discussing key findings and identifying areas for further research.