The interplay of genes and environment on children's development is a complex dynamic process. As behavior geneticists begin to model protective as well as risk factors, and interactive as well as main effect influences, development is elucidated. It was hypothesized that positive parenting, a quality home environment, and high family cohesion would moderate the heritability of three components of temperament: Effortful Control, Negative Affectivity, and Extraversion/Surgency. Participants were drawn from the Wisconsin Twin Project and consisted of 1573 twins (51% boys), 88.5% Caucasian, M=7.93 years (SD=0.87). Higher order composites for the parenting and family environment moderators were formed from mother and father reports of Behavior Management Self-Assessment, Child Rearing Practices Report, Family Assessment Device, and Family Conflict Scale. Measures of the home environment (LEOS Living Environment Observation Scale and CHAOS Confusion, Hubbub, and Order Scale) were not composited due to the nature of the variables. Correlational analyses showed a majority of the temperament and environmental measures to be correlated (rs = -.49-.57). For Effortful Control, Negative Affectivity, and Extraversion/Surgency, estimates for the heritability and nonshared environment were 0.60 and 0.40, 0.80 and 0.20, and 0.59 and 0.41, respectively, with no significant main effects of the shared environment. Models incorporating environmental moderation of these estimates yielded parenting as a significant moderator for Negative Affectivity, LEOS for Effortful Control and Extraversion/Surgency, and CHAOS for Effortful Control and Extraversion/Surgency. Results suggest that the quality of the family environment may act as a permissive or determinative influence on the heritability and expression of temperament. Future analyses include the examination of interactive genetic influences. These findings underscore the importance of shared environment, and support the recent literature on the benefits of positive influences on children's development.