A "welfare-based defense" of a practice involving nonhuman animals presents the examined practice as promoting the animal's own interests. Such justifications surface in relation to various interactions between human and nonhuman animals. Sometimes such arguments appear persuasive. Sometimes they form self-serving rationalizations. This paper attempts to clarify and specify the distinction between plausible and dubious applications of such arguments. It then examines (and rejects) a detailed welfare-based defense of zoos.