Recent research shows that from an early age, infants appear to attribute mental states such as goals, dispositions, perceptions, and beliefs to agents—whether human or nonhuman. Agents are entities that can detect their environment and exert control over their actions. In the present chapter, we review evidence on infants’ understanding about nonhuman agents. We describe results highlighting certain featural information and behavioral cues infants may use to identify agents. In light of the empirical results, we discuss our theoretical account and speculate on the learning mechanisms involved in early psychological understanding.