This paper will review the literature on the rate, stability, and outcomes associated with externalizing behavior problems prior to kindergarten entry. Bronfenbrenner's (The ecology of human development. Cambridge, MA: Harvard University Press) ecological framework will be used to present the factors related to the onset and persistence of externalizing behavior problems in young children. Behavior problems prior to school entry are somewhat developmentally appropriate and most can be resolved within the classroom or child care setting. Intervention for children with moderate to severe behavior problems in early childhood is crucial because behavior problems are likely to persist into elementary school leading to a variety of social and academic concerns. Steps will be presented to help teachers determine whether or not a referral to a specialist is needed and locate an appropriate specialist.