What kinds of moral challenges arise from encounters between species in laboratory science? Animal Ethos draws on ethnographic engagement with academic labs in which experimental research involving nonhuman species provokes difficult questions involving life and death, scientific progress, and other competing quandaries. Whereas much has been written on core bioethical values that inform regulated behavior in labs, Lesley A. Sharp reveals the importance of attending to lab personnel’s quotidian and unscripted responses to animals. Animal Ethos exposes the rich—yet poorly understood—moral dimensions of daily lab life, where serendipitous, creative, and unorthodox responses are evidence of concerted efforts by researchers, animal technicians, veterinarians, and animal activists to transform animal laboratories into moral scientific worlds.