Bullying has emerged as a distinct, pervasive subset of peer aggression that affects youth worldwide. Although bullying is a complex phenomenon, some subgroups of youth are at escalated risk based on individual characteristics, skill deficits, and peer group or societal norms. Therefore, the field needs reliable measurement systems, precise understanding of social-ecological risk and protective factors, and effective prevention and intervention approaches. This special issue addresses bullying from a social-ecological framework. It examines measurement issues, as well as risk and protective factors, with an emphasis on the disproportionate involvement of specific subpopulations of school-aged youth. It concludes with a series of original articles on expanding intervention targets through evidence-based practices for reducing bullying among students from early childhood through high school. Ultimately, this special issue should serve as a call-to-action for increased research on predictive and protective factors associated with bullying involvement, as well as increased intervention and prevention efforts.