In this chapter, I discuss spaces crucial to transgender and gender non-binary (trans) athlete welfare: binary-gendered locker rooms. Although empirical evidence suggests that trans people face significant barriers to accessing locker rooms, little research has explored how experiences in locker rooms impact trans participation in sport and physical activity. Without investigating locker rooms as a site of trans exclusion, I argue, it will be difficult to advance trans athlete welfare. Drawing on in-depth interviews, I explore first how trans people experience binary-gendered locker rooms as spaces of surveillance and scrutiny. Second, I examine and assess several initiatives being used by institutions and facilities to advance trans inclusivity in locker rooms. This chapter offers both a theoretical exploration of the ways in which binary-gendered locker rooms impact trans athlete welfare, as well as suggestions for a practical repertoire of interventions for making locker rooms, and thus physical activity, more trans inclusive.