Learning to Save the World provides an innovative analysis of how individuals inhabit, refuse, and reconfigure the contours of global health. In 2001, Botswana's government, faced with one of the highest HIV prevalence rates in the world, committed itself to sub-Saharan Africa's first free public HIV treatment program. US-based private foundations and medical schools offered support to demonstrate the feasibility of public HIV treatment in Africa. Given US interest and investment in global health, this support created opportunities for US physicians and medical trainees to interact with local practitioners, treat patients, and shape health policy in Botswana. Although global health has emerged as a powerful call to planetary moral action, the nature of this exhortation remains unclear. Is global health a new movement for social justice, or is it neocolonial, creating new dependencies under the banner of humanitarianism? Betsey Behr Brada shows that global health is a frontier, an imaginative framework that organizes the space, time, and ethics of encounter. Learning to Save the World reveals how individuals and collectivities engaged in global health—visiting experts as well as local clinicians and patients—come to regard themselves and others in terms of this framework.