Several intellectual and developmental disorders first emerge or are identified during the preschool period, when children are 3 to 6 years old and when a broad array of skills and capacities are expected to emerge and develop. Early literacy and numeracy capacities, sustained attention, behavioral and emotional regulation abilities, and social skills develop precipitously during this time. Underlying many of these domains of abilities is executive function, and problems with executive functioning are often concomitant with the intellectual and developmental disorders that are identified during preschool. This entry defines executive functioning, provides an overview of the intellectual and developmental disorders that often are first identified during the preschool period, discusses their association with executive functioning, and highlights some approaches for addressing executive function deficits.