Existing evidence suggests that problem/pathological gambling is frequently associated with a broad range of substance or behavioural addictions. Unfortunately, little is known regarding the role that disorders play in the development and maintenance of gambling dependence. For example, how these affect gambling and vice versa, or the extent to which pathological gambling and disorders co-occur, that is, are truly comorbid. Moreover, few studies have investigated biological, psychological, social and environmental influences involved in comorbidity relationships. Furthermore, it is not known whether psychiatric or substance disorders directly interfere with the efficacy of gambling treatment. This chapter aims to improve our understanding of how disorders interact, both in terms of determining the most appropriate treatment and improving treatment outcomes. It fo-cuses on the correlation between disordered gambling and substance abuse; discusses the literature and gives an overview of empirical research into such comorbidity, including diagnostic and screening instruments; and examines the implications for prognosis and treatment and provides future recommend.