Surfacing in the mid-twentieth century, yet shrouded in social stigma, transgender medicine is now a rapidly growing medical field. In , stef shuster makes an important intervention in how we understand the development of this field and how it is being used to “treat” gender identity today. Drawing on interviews with medical providers as well as ethnographic and archival research, shuster examines how health professionals approach patients who seek gender-affirming care. From genital reconstructions to hormone injections, the practice of trans medicine charts new medical ground, compelling medical professionals to plan treatments without widescale clinical trials to back them up. Relying on cultural norms and gut instincts to inform their treatment plans, shuster shows how medical providers’ lack of clinical experience and scientific research undermines their ability to interact with patients, craft treatment plans, and make medical decisions. This situation defies how providers are trained to work with patients and creates uncertainty. As providers navigate the developing knowledge surrounding the medical care of trans folk, offers a rare opportunity to understand how providers make decisions while facing challenges to their expertise and, in the process, have acquired authority not only over clinical outcomes, but over gender itself.