In recent years, deficits in emotion regulation have been studied as a putative maintaining factor and promising treatment target in a broad range of mental disorders. This article aims to provide an integrative review of the latest theoretical and empirical developments in this rapidly growing field of research. Deficits in emotion regulation appear to be relevant to the development, maintenance, and treatment of various forms of psychopathology. Increasing evidence demonstrates that deficits in the ability to adaptively cope with challenging emotions are related to depression, borderline personality disorder, substance-use disorders, eating disorders, somatoform disorders, and a variety of other psychopathological symptoms. Unfortunately, studies differ with regard to the conceptualization and assessment of emotion regulation, thus limiting the ability to compare findings across studies. Future research should systematically work to use comparable methods in order to clarify the following: which individuals have; what kinds of emotion regulation difficulties with; which types of emotions; and what interventions are most effective in alleviating these difficulties. Despite some yet to be resolved challenges, the concept of emotion regulation has a broad and significant heuristic value for research in mental health.