The average American has yet to encounter new information about the importance of "healthy sperm" and the "male biological clock." That is because basic medical knowledge about how men matter when it comes to reproductive outcomes, from miscarriages to childhood illnesses, has only recently begun to be produced. This gap in knowledge about men is only more glaring when one considers the enormous efforts to understand and treat women's reproductive bodies over the past century. GUYnecology asks: What took so long? Why are biomedical researchers only now asking questions about how men's age and bodily health affect reproductive outcomes? Weaving together historical materials and qualitative interviews, Rene Almeling examines the history of medical knowledge-making about men's reproductive health and its consequences for individuals. From a failed nineteenth-century effort to launch a medical specialty called andrology to the contemporary science of paternal effects, a lack of medical specialization around men's reproductive bodies has resulted in obliviousness about men's role in reproductive outcomes. Sifting through media messages and analyzing the stories of individual men and women, Almeling demonstrates how this historical gap in attention shapes reproductive politics today.