Bullying remains a significant public health concern, with more than one in five students reporting victimization (National Center for Education Statistics 2024). Involvement in bullying—whether as aggressor, target, or bystander—is linked to adverse social, emotional, and academic outcomes, as well as broader school climate concerns. This chapter provides an overview of bullying and related behaviors across childhood and adolescence, including conceptualization, prevalence, and impact. The chapter also addresses associated forms of aggression such as cyberbullying, harassment, sexual harassment, and microaggressions. Research consistently demonstrates strong associations between bullying involvement and depressive symptoms, anxiety, psychosomatic complaints, and sleep problems, with longitudinal evidence highlighting lasting effects (e.g., Camerini et al., 2020; Haltigan & Vaillancourt, 2017). The lasting impact of bullying has driven growing emphasis on school-based strategies to prevent harm, and the chapter concludes with a summary of bullying prevention and intervention approaches.