Anxiety, depression, and somatic complaints are a common set of comorbid problems in children and adolescents. This "internalizing cluster" is highly prevalent, impairing during youth and into adulthood, and has substantial impacts on health-care systems. Fortunately, these problem areas may share several etiological factors and, thus, respond to similar interventions. In this paper, we present (a) the rationale for focusing on this cluster, (b) clinical theory on transdiagnostic processes uniting these problems, (c) description of core treatment techniques for this group, with a description of clinical outcomes for two sample cases, and (d) implications of this approach for new transdiagnostic treatment development and everyday clinical practice. (Contains 2 tables, and 2 figures.)