This study investigates possible individual and class correlates of defending and passive bystanding behavior in bullying, in a sample of 1,825 Italian primary school (mean age = 10 years 1 month) and middle school (mean age = 13 years 2 months) students. The findings of a series of multilevel regression models show that both individual (e.g., provictim attitudes and perceived peer pressure for intervention) and class characteristics (e.g., class provictim attitudes, peer injunctive norms, and descriptive norms) help explain defending and passive bystanding behavior in bullying. These results significantly expand previous findings in this field, by demonstrating the need for a social-ecological approach to the study of the different aspects of bullying. Implications for antibullying programs are discussed. (Contains 3 tables and 1 figure.)