Until recently clinical psychology has been mainly concerned with what is defined as deviant and/or maladaptive mental states. In this chapter, we present a new model for sustainable mental health that allows for balanced psychological treatment. The model is based on a growing body of research demonstrating that mental illness and mental well-being are related but distinct dimensions of mental health. Further research shows that well-being actually reduces the risk of mental illness. An important component in the model is that sustainable mental health incorporates well-being as an essential mental health outcome in addition to and alongside mental illness. The model also proposes adaptation processes that are essential in the regulation of mental well-being and mental illness. Psychological treatments and interventions are placed on a spectrum targeting either barriers or resources for successful adaptation or a combination of both. Evidence of the impact of psychological treatments that fit well with the model such as Acceptance and Commitment Therapy and Life-review therapy in the context of public mental health is presented. The advantages of the model are twofold. Firstly, it surpasses a simplistic dichotomy of ‘positive’ versus ‘negative’ approaches, and secondly, it offers an integrative perspective for practitioners.