A sweeping study that reveals how conservation science does more than simply protect by inadvertently making nature valuable in new ways.  Climate change and other environmental transformations are causing species to go extinct at accelerating rates. What, then, should a science of saving nature look like? In Rarities, Zoe Nyssa traces how conservation emerged as a distinct scientific endeavor in the United States over the twentieth century and how this history has shaped environmental research practices and policy today. Drawing on archival and ethnographic research with leading conservation labs and programs, Nyssa explores how conservation science appears to generate contradictory, even counterintuitive, results as scientists, policymakers, and the public all take up, respond to, and repurpose scientists’ ideas about rarity, vulnerability, and endangerment. The designation of new nature reserves can lead to increased poaching and habitat destruction. The listing of a species as endangered fuels their black-market consumption as pets, food, or luxury items. Protection of natural resources can push resource extraction into unprotected areas. Other effects are less simple to calculate; persuading the public to care about one species might siphon support for another, and paying for one kind of conservation behavior can discourage other forms of conservation activity.  The science of saving nature spans a century of work by ecologists and others to develop a scientific basis for conservation. Yet Nyssa shows how their efforts to understand the natural world in terms of endangerment and extinction unleashed new ways for nonscientists to experience and understand nature as well. The scientific values that emerge, she argues, can transform the complex interconnections between human and nonhuman life. Rarities offers a framework for understanding these surprising socio-ecological dynamics and why they matter, both for contemporary science and for the planet.