Transdiagnostic interventions make use of eclectic treatment strategies to address multiple diagnostic problem sets linked by common underlying etiological or maintaining mechanisms. A good transdiagnostic treatment relies on strategies with empirical support and is flexible enough to accommodate diverse problems. As such, transdiagnostic treatments have numerous potential advantages over traditional approaches, including increased efficiency, practicality, efficaciousness, and effectiveness. Translation of transdiagnostic therapies to youth populations is in its nascent stages. This introduction reviews the special series in adaptations of transdiagnostic treatments to youth population. It will define transdiagnostic therapies, discuss potential advantages of such an approach, and then review each of the special series articles.