In this introductory chapter, I provide a framework for a transdiagnostic approach to understanding the risk and protective factors for positive family and peer relationships of children and adolescents with neurodevelopmental disorders (NDs). I describe how the names of the disorders and the criteria for diagnosing them have changed over time and provide examples that show that there is an overlap in the symptoms of each disorder. I argue that the changing diagnostic criteria and symptom overlap affect the prevalence of the disorders and the extent of comorbidity between the disorders. I review research that supports a bi-directional relationship between transdiagnostic characteristics of ND youth (i.e., difficulties with self-regulation, adaptive skills, academic achievement and performance, and social skills) and their family and peer relationships.