This dissertation is based on seventeen months of ethnographic fieldwork that followed the development and diffusion of extended-cycle hormonal contraception, or birth control that is designed to eliminate monthly bleeding. It encompassed several sites and multiple constituencies: a clinical trial, documented medical conferences, users, potential users, and refusers of the pharmaceuticals, along with key academic and popular proponents of their adoption. Extended-cycle contraception is a critical topic because this new generation of pills, IUDs, shots, and implants is not only refiguring the length of women's cycles, but it is also augmenting the extent to which its users' bodies are medicalized, or subjected to a type of manipulation and regulation that was previously impossible. No longer just for pregnancy prevention, these regimens are increasingly touted as elective enhancement technologies that may improve on the human design, on the one hand, and as crucial preventative medicine for diseases such as reproductive cancers, on the other hand. Remarkably, these pharmaceuticals are as socially complex as they are chemically--they may facilitate the renegotiation of constructions of womanhood, nature, and progress.