Lessons were learned with trans women who participated (as volunteers and investigators) in trials of HIV pre-exposure prophylaxis (PrEP). Trans women are not men. Compared with men who have sex with men, trans women trial participants were more likely to be involved with transactional sex, had more sexual partners, and were less likely to have PrEP medications detected in blood. Trans women define themselves differently in different cultures. One best practice is to ask at least 2 gender questions: sex assigned at birth and current gender. More information is needed to fully situate PrEP efficacy for trans women, including analysis of drug-drug interactions between PrEP medications and feminizing hormones and PrEP drug penetration into neovaginal tissues. Including trans women in studies is helpful only if their participation is specifically reported, as could occur in a table of baseline characteristics of the enrolled cohort. Gender-affirming care is important to foster appropriate uptake and use of PrEP. Such care includes use of preferred pronouns and names, safety to use the bathroom of choice, and access to gender-affirming hormone therapy and surgery. The consistent finding that PrEP works when taken across diverse populations having diverse practices related to gender, sexual intercourse, and hormone use provides a basis for offering PrEP to people at substantial risk of acquiring HIV although some subgroups may not have been fully represented in trials. Nonetheless, specific PrEP implementation science for trans women (and men) is essential to develop best practices for PrEP delivery and use.