The eligibility of DSD (Differences of Sexual Development)- and trans-athletes in the female category in elite sports is a controversial issue and raises fundamental questions of scientific and ethical kinds. The scientific questions relate among other things to the impact of elevated testosterone levels in the development and execution of athletic performance in various sports, and the ethical questions concern the tension between the right of individuals to take part according to their legal gender and the right of all athletes to fair competition in their category. The underlying general questions concern the meaning and function of categorizing athletes in sports, and competition fairness. In this session, two international experts, Professor of Sport and Exercise Science Yannis Pitsiladis and bioethicist and Professor Silvia Camporesi, address the issue from complementary perspectives. Dr. Pitsiladis examines the justification in some sports for deeming transgender women athletes ineligible in the female class, and Dr. Camporesi discusses similar questions in the case of DSD athletes. These are topical issues that should be of interest to the broad sport science community.