ABSTRACT. This paper reviews and critiques the growing literature on the distinction between reactive and proactive aggression in children and adolescents. Empirical findings suggest that the subtypes of aggression are (a) preceded by different familial precursors, (b) associated with different behavioral outcomes, (c) driven by different social–cognitive and emotional processes, and (d) related to different social experiences. Because measurement difficulties have been a prominent concern in the study of reactive and proactive aggression, a discussion of various assessment approaches is included. Suggestions are made for future research directions, including a greater use of observational and laboratory-based methods, more longitudinal designs, and a greater focus on the careful assessment of the subtypes of aggression.