This chapter begins with a brief history of women’s exclusion from organized sports in the United States, and describes the evidence for the importance and value of Title IX. Reasons for continued sex segregation in sports are described. The Transgender Exigency begins with the famous case of Renée Richards, and I describe the scientific research concerning athletic performance and testosterone given the definitive role testosterone levels play in regulatory definitions of male and female in the evolving policies of the International Olympic Committee and the NCAA. The final section focuses on the disparity of high school regulatory definitions.