People retrieve episodic memories about specific earlier events that happened to them. Accordingly, researchers have sought to evaluate the hypothesis that nonhumans retrieve episodic memories. The central hypothesis of an animal model of episodic memory is that, at the moment of a memory assessment, the animal retrieves a memory of the specific earlier event. Testing this hypothesis requires the elimination of nonepisodic memory hypotheses. A number of case studies focus on the development of animal models of episodic memory, including what-where-when memory, source memory, item-in-context memory, and unexpected questions. Compelling evidence for episodic memory comes from studies in which judgments of familiarity cannot produce accurate choices in memory assessments. These approaches may be used to explore the evolution of cognition.