Infanticide in the natural world might be a relatively rare event, but as Amanda Rees shows, it has enormously significant consequences. Identified in the 1960s as a phenomenon worthy of investigation, infanticide had, by the 1970s, become the focus of serious controversy. The suggestion, by Sarah Hrdy, that it might be the outcome of an evolved strategy intended to maximize an individual’s reproductive success sparked furious disputes between scientists, disagreements that have continued down to the present day. Meticulously tracing the history of the infanticide debates, and drawing on extensive interviews with field scientists, Rees investigates key theoretical and methodological themes that have characterized field studies of apes and monkeys in the twentieth century. As a detailed study of the scientific method and its application to field research, The Infanticide Controversy sheds new light on our understanding of scientific practice, focusing in particular on the challenges of working in “natural” environments, the relationship between objectivity and interpretation in an observational science, and the impact of the public profile of primatology on the development of primatological research. Most importantly, it also considers the wider significance that the study of field science has in a period when the ecological results of uncontrolled human interventions in natural systems are becoming ever more evident.