Collective efficacy, defined as informal social controls that operate under social norms of trust, is an emerging theoretical concept that has been applied to explain violence rates in neighborhoods, affiliation with deviant peers, partner violence, and adolescent delinquency. This study employed a multilevel design to examine the association between collective efficacy at the class-level and individual-level bullying perpetration and victimization using survey data from 1,729 Greek students, aged 11 to 14 years. School class collective efficacy was defined as cohesion and trust among class members combined with their willingness to intervene in the case of aggressive or bullying incidents. Our findings indicate that individual-level victimization is more frequent in classes with lower levels of collective efficacy. We conclude that the notion of collective efficacy might also prove useful in explaining bullying involvement. (Contains 3 tables.)