The purpose of the current study was to determine the genetic and environmental contributions to the development of prosocial behavior in children using a population of 356 twins at 8 years of age. The study also aimed to examine whether qualities of parenting (specifically authoritarian and authoritative parenting styles) were phenotypic predictors of prosocial behavior. Both parent-reports and objective ratings of global prosocial behavior were used. Results supported prosocial behavior as a genetically-influenced trait with heritability estimates of 44% and 68% for parent reported and observed prosocial behavior, respectively. Data also suggested prosocial behavior as an environmentally-influenced trait. As hypothesized, authoritative parenting was moderately correlated with parent-reported prosocial behavior and authoritarian parenting was found to be low-to-moderately negatively correlated with parent-reported prosocial behavior. Multi-variable regressions demonstrated that authoritative parenting was significantly predictive of increased parent-reported prosocial behavior but authoritarian parenting was not predictive of decreased parent reported prosocial behavior. However, observed prosocial behaviors were largely independent of both authoritative and authoritarian styles of parenting.