During the twentieth century, opportunities for exercise, sports, and recreation grew significantly for most girls and women in the United States. Female physical educators were among the key experts who influenced this revolution. Drawing on extensive archival research, this book examines the ideas, experiences, and instructional programs of white and black female physical educators who taught in public schools and diverse colleges and universities, including coed and single-sex, public and private, and predominantly white or black institutions. Working primarily with female students, women physical educators had to consider what an active female could and should do in comparison to an active male. Applying concepts of sex differences, they debated the implications of female anatomy, physiology, reproductive functions, and psychosocial traits for achieving gender parity in the gym. Teachers' interpretations were contingent on where they worked and whom they taught. They also responded to broad historical conditions, including developments in American feminism, law, and education, society's changing attitudes about gender, race, and sexuality, and scientific controversies over the nature and significance of sex differences. While deliberating fairness for female students, white and black women physical educators also pursued equity for themselves, as their workplaces and nascent profession often marginalized female and minority personnel. Questions of difference and equity divided the field throughout the twentieth century; while some women teachers favored moderate views and incremental change, others promoted justice for their students and themselves by exerting authority at their schools, critiquing traditional concepts of "difference," and devising innovative curricula. Connecting the history of science, race and gender studies, American social history, and the history of sport, this book sheds new light on physical education's application of scientific ideas, the politics of gender, race, and sexuality in the domain of active bodies, and the enduring complexities of difference and equity in American culture.