The hierarchical competing systems model (HCSM) provides a framework for understanding the emergence and early development of executive function--the cognitive processes underlying the conscious control of behavior--in the context of search for hidden objects. According to this model, behavior is determined by the joint influence of a developmentally invariant habit system and a conscious representational system that becomes increasingly influential as children develop. This article describes a computational formalization of the HCSM, reviews behavioral and computational research consistent with the model, and suggests directions for future research on the development of executive function.