Samples of 758 children in the United States and 220 children in Finland were interviewed and tested in each of 3 years in an overlapping longitudinal design covering Grades 1 to 5. For girls in the United States and boys in both countries, TV violence viewing was significantly related to concurrent aggression and significantly predicted future changes in aggression. The strength of the relation depended as much on the frequency with which violence was viewed as on the extent of the violence. For boys the effect was exacerbated by the degree to which the boy identified with TV characters. Path analyses suggested a bidirectional causal effect in which violence viewing engenders aggression, and aggression engenders violence viewing. No evidence was found that those children predisposed to aggression or those with aggressive parents are affected more by TV violence. However, a number of other variables were found to be correlates of aggression and violence viewing. The most plausible model to explain these findings seems to be a multiprocess model in which violence viewing and aggression affect each other and, in turn, are stimulated by related variables. Observational learning undoubtedly plays a role, but its role may be no more important than the attitude changes that TV violence produces, the justification for aggressive behavior that TV violence provides, or the cues for aggressive problem solving that it furnishes.