The fairplayer.manual is a school-based program to prevent bullying. The program consists of fifteen to seventeen consecutive ninety-minute lessons using cognitive-behavioral methods, methods targeting group norms and group dynamics, and discussions on moral dilemmas. Following a two-day training session, teachers, together with skilled fairplayer.teamers, implement fairplayer.manual in the classroom during regular school lessons. This chapter offers a summary of the program's conception and underlying prevention theory and summarizes the results from two evaluation studies. Standardized questionnaires showed a positive impact of the intervention program on several outcome variables.