Mental disorders impose an enormous burden on society, accounting for almost one in three years lived with disability globally. •In addition to their health impact, mental disorders cause a significant economic burden due to lost economic output and the link between mental disorders and costly, potentially fatal conditions including cancer, cardiovascular disease, diabetes, HIV, and obesity.•80% of the people likely to experience an episode of a mental disorder in their lifetime come from low- and middle-income countries.• Two of the most common forms of mental disorders, anxiety and depression, are prevalent, disabling, and respond to a range of treatments that are safe and effective. Yet, owing to stigma and inadequate funding, these disorders are not being treated in most primary care and community settings.