The early education field increasingly is recognizing the key role played by young children's executive function (EF) skills, generally defined as the cognitive abilities that consciously support goal-directed behaviors. To provide the field with an overview of research conducted on this topic over the past 15 years, we review research on the traits and skills that fall under the broader umbrella of preschool EF and the role it plays in young children's developmental and academic outcomes. Also addressed are the child, environmental, activity-related, and curricular factors potentially impacting the development of EF and some EF-related topics for which additional research is needed. Finally, we provide practical and psychometric information regarding six examples of measures that focus on assessing preschoolers' EF skills. This report can serve as a resource for early childhood researchers and practitioners who are interested in understanding EF development during the early years. By highlighting some topics for which additional research is needed and providing information regarding examples of valid and reliable measures to assess EF in children ages 3-5 years, we hope this report also will serve as a springboard for future studies related to preschool EF. (author abstract)