Relationship functioning and individual mental health and well-being are strongly associated with one another. In this article, we first review the cross-sectional and longitudinal associations between relationship discord and various types of psychopathology, We then review findings suggesting that relationship discord is associated with poorer outcome for individual-based treatments for psychopathology and that, generally, relationship discord does not improve following individual-based treatments for psychopathology. Finally, we present a model for conceptualizing work with couples in which one partner has a psychiatric disorder and review the efficacy of couple-based interventions in the treatment for psychiatric disorders, with a focus on substance-related, mood, and anxiety disorders.