This book explores the notion of endangerment which stands at the heart of a network of concepts, values and practices dealing with objects considered threatened by extinction, and with the procedures aimed at preserving them. It looks at some of the fundamental ways in which this process involves science, but also more than science: not only data and knowledge and institutions, but also affects and values. With a focus on endangerment sensibility, it encapsulates tensions between the normative and the utilitarian, the natural and the cultural.