Common mental disorders are responsible for up to 10% of the total global disease burden. The growing evidence base for the efficacy and cost-effectiveness of treatments for these disorders raises the possibility of delivering huge health and economic benefits. However, delivering these treatments in resource-constrained settings is challenging. At least one-third of all patients seen in primary care in low- and middle-income countries present with common mental disorders. The majority are not recognised or are ineffectively treated. To address this problem, WHO advocates integrating mental health in primary care. However, the limited evidence base has impeded efforts to develop such services.