Abstract We provide evidence for the claim that before young children construe human action in terms of beliefs and desires they understand action only in terms of simple desires. This type of naive psychology—a simple desire psychology— constitutes a coherent understanding of human action, but it differs from the belief-desire psychology of slightly older children and adults. In this paper we characterize what we mean by a simple desire psychology and report two experiments. In Experiment 1 we demonstrate that 2-year-olds can predict actions and reactions related to simple desires. In Experiment 2 we demonstrate that many 2-year-olds pass desire reasoning tasks while at the same time failing belief reasoning tasks that are passed by slightly older children, and that are as comparable as possible to the desire tasks they pass with ease.