Executive function (EF) refers to the set of neurocognitive skills involved in goal-directed problem solving, including working memory, inhibitory control, and set shifting/flexibility. EF depends importantly upon neural networks involving prefrontal cortex, and continues to improve into early adulthood, although major advances in EF occur during the preschool period. Individual differences in EF are increasingly recognized as a key predictor of long-term cognitive and social developmental outcomes. Research suggests that EF is influenced by both distal and proximal factors in development (e.g., socioeconomic status, culture, language, caregiving, gene–environment interactions, and sleep). Importantly, EF can be trained, with corresponding changes to brain structure and function. In this chapter, we review the structure of EF, including “hot EF” (EF in motivationally significant contexts), age-related changes, atypical development, measurement issues, theories of underlying mechanisms, outcomes associated with EF, influences on EF development, and the recent emergence of training studies.