Abstract— The tripartite model proposed by L. A. Clark and D. Watson (1991) describes the common and unique features of anxiety and depression by delineating their relation with the dimensions of negative affect, positive affect, and physiological hyperarousal. Although this model was initially developed for adults, researchers have been increasingly interested in its applicability to a younger age range. However, several problems have hindered meaningful systematic research and forestalled conclusions regarding the validity of the model in childhood and adolescence. This article provides a review of these difficulties, along with a number of recommendations for future research, in order to enhance a firm understanding of the development of the tripartite dimensions, their interrelations, and their relations to anxiety, depression, and other Axis I disorders across the life span.