Numerous behavioral genetic studies call attention to the strong and pervasive genetic influence on developmental characteristics. However, this research has been criticized for its use of poor environmental measures and a failure to examine the complex processes that are a hallmark of research in child development. This study addresses this criticism by examining the genetic and environmental components of parent-child interactions. Mother, father, and 2 adolescent siblings (10-18 years) from each of 675 families were observed interacting in 10-min dyadic problem-solving sessions. 6 groups of siblings that differed in genetic relatedness were examined (MZ and DZ twins, full siblings in nondivorced families; full, half, and unrelated siblings in stepfamilies). Results suggest a greater genetic component to adolescent behavior than to parent behavior. Both adolescent and parent behavior showed strong effects of nonshared environment, even after error of measurement was removed.