Children displaying high levels of aggression have repeatedly been shown to be at significant risk for continued behavior problems and other social and emotional challenges throughout their lifetimes. The current project includes two papers that examine factors contributing to the development and maintenance of aggression in preschool-aged children, especially focusing on preschool boys. The first paper reviews theoretical and empirical literature addressing the development of aggressive behavior problems. Specific attention is given to influences within the child's family environment, including positive parental involvement, harsh discipline practices, and play activities of the child both individually and jointly with his or her parent or caregiver. The second paper presents results of an empirical investigation of the relationship between parent behaviors during parent-child interactions and teacher-reported problem behaviors in preschool boys. A stratified sample of 34 three- to five-year old boys and their primary caregivers were observed in their homes engaged in unstructured free-play and a problem-solving task. Behaviors of primary caregivers in each interaction were examined in relationship to teachers' ratings of the boys' externalizing behaviors in a child care setting. Parenting characteristics in the play, but not problem-solving, interaction were found to have a statistically significant relationship with boys' externalizing scores. Positive characteristics of the caregiver in play, such as warmth and sensitivity to the child, accounted for a statistically significant amount of variance in boys' teacher-reported externalizing scores beyond that accounted for by the negative characteristics, such as intrusiveness and hostility. The findings are discussed in relation to previous literature that has addressed both the development of behavior problems in young children and the role of parent-child play interactions in child development. Clinical implications for this population are also discussed.