The overarching goal of this article is to examine the current best evidence for assessing bipolar disorder (BPD) in children and adolescents and provide a comprehensive, evidence-based approach to diagnosis. Evidence- based assessment strategies are organized around the "3 Ps" of clinical assessment: Predict important criteria or developmental trajectories, Prescribe a change in treatment choice, and inform Process of treating the youth and his/her family. The review characterizes BPD in youths-specifically addressing bipolar diagnoses and clinical subtypes; it then provides an actuarial approach to assessment using prevalence of disorder, risk factors, and questionnaires; discusses treatment thresholds; and identifies practical measures of process and outcomes. The clinical tools and risk factors selected for inclusion in this review represent the best empirical evidence in the literature. By the end of the article, clinicians will have a framework and set of clinically useful tools with which to effectively make evidence-based decisions regarding the diagnosis of BPD in children and adolescents.