Since the 1950s, transgender and gender nonconforming individuals have emerged as polemic and sensationalized figures in Western media accounts. Some of the controversy has centered on their participation in sex-divided sporting spaces since Rene Richards groundbreaking appearance on the Women's Tennis Association tour in 1977. Sport in the West, and much of the world is organized in terms of taken-for-granted assumptions of binary and hierarchical sex difference by virtue of sex segregated sporting spaces and grossly unequal cultural and economic spaces. There is, at times, considerable tension and overlap among and between transgender and transsexual persons and self-definitions rarely conform to hard and fast categorical distinctions. Concerns about transgender participation in sport tend to crystallize around assumptions about exposure to testosterone – either prior to or as part of transitioning – as conferring an unfair advantage. This chapter provides an overview of the key concepts discussed in this book.