Animal Ethos is framed by efforts to unearth and decipher moral thought and action in experimental forms of laboratory science. More specifically, as an ethnographic project, it attends to the ordinary, everyday, or mundane aspects of human-animal encounters in lab research. I purposefully distinguish between bioethics—or regulatory principles (that may be codified as law) that determine what one can and cannot do experimentally—and morality, namely, the personal and private musings of lab personnel whose research and livelihoods hinge on the use of animals for furthering medico-scientific knowledge. I consider moral thought in science as an imaginative project, where unexpected conundrums may challenge one to pause and consider the limits of dominant ethical frameworks. Such reconsiderations lie at the heart of the making of oneself as a moral being, where the core questions I’ve posed to involved lab personnel might be phrased as “how do you think of your work when you go home at the end of the day?” or, as animal activists might restate it, “how do you live with yourself, knowing what you do?” I underscore here that I am not interested in whether one is practicing ethical science but, instead, in the private, subjective (and interspecies) dimensions of ongoing, often lifetime, work in which one engages, and how this plays out in personal efforts to forge a moral sense of self against the backdrop of scientific pursuits. My earlier ethnographic engagements in specialized realms of transplantation—as described in my works Strange Harvest (2006, University of California Press) and The Transplant Imaginary (2013, University of California Press)—taught me that, whereas lab researchers readily convey complex understandings of regulations that define “ethical research,” there exists no similarly robust lexicon for describing personal experience and sentiment. Indeed, research personnel often explained to me that morality is the purview of philosophy and religion, not science. As I slowly came to realize, though, when lab personnel talk about animals, which they do openly and often, they shift to a highly personalized, moral register. With this in mind, Animal Ethos is not a study of lab animals, but instead employs “animal talk,” so to speak, as a method for accessing how lab scientists think about the sociomoral underpinnings of what they do. As Claude Lévi-Strauss so famously proclaimed, “animals are good to think.” With this adage in mind, it is through the animal that I access moral thought and action among those whose careers rely on non-human species as essential research participants.