As described in Chap. 2, systematic reviews and meta-analyses have been conducted on different topics related to bullying and anti-bullying interventions. Among them, the most comprehensive searches and analyses were carried out by Farrington and Ttofi (2009), who reviewed 53 evaluations published in 89 reports. They found that, after these anti-bullying interventions, overall, bullying perpetration decreased about 20-23%, and bullying victimization dropped about 17-20%. Thus, anti-bullying programs can protect children from this kind of aggression. Nevertheless, not all programs or components are equally effective. This chapter will review important anti-bullying interventions conducted in different geographic areas mostly at a national or regional level with large samples and rigorous designs (see also Baldry and Farrington 2007).According to the meta-analysis conducted by Farrington and Ttofi (2009), certain components of anti-bullying programs are effective in reducing perpetration or victimization. Figure 5.1 shows the components that were found to work better than others in reducing perpetration, victimization, or both.Farrington and Ttofi (2009) found that there were some components that worked best in reducing both perpetration and victimization. Among them, parent training, in which information about bullying and anti-bullying programs was provided, was found to be effective. More intensive and longer programs (for both teachers and students) worked best. Cooperative group work among experts in which information was exchanged, common aims were established or solutions to different problems were discussed, was also useful. Disciplinary methods involving the elaboration and application of new rules, including sanctions for bullying were also effective in reducing perpetration and victimization.Some features were found to be effective in reducing perpetration or victimization only. The decrease in perpetration was greater in interventions that included teacher training and a whole-school anti-bullying policy with classroom rules,