The present paper serves as the first systematic review of the training, methodologies, and outcomes reported in the professional development (PD) literature for paraprofessionals working with students with or at risk for externalizing behavior disorders. A total of 16 investigations including 332 paraprofessionals and 852 children and adolescents were reviewed and coded on 44 variables across four dimensions (i.e., PD components, intervention components, methodologies used, and outcomes reported). Strengths of the literature were inclusion of multicomponent PD, training on implementation, paraprofessional characteristics, and inter-rater reliability estimates. All studies reported paraprofessional and/or student outcomes; however, the details of PD components and interventions delivered varied. The majority of the studies used single-case designs or descriptive case studies to evaluate effectiveness. Weaknesses were lack of inclusion and exclusion criteria, student characteristics, adult experiential learning methods, monitoring of implementation fidelity, and use of statistical testing. Implications for research and practice are offered. [For the corresponding grantee submission, see ED605568.]