Mental illnesses are highly prevalent worldwide but most countries allocate less than 2% of their health budgets to mental health. Effective and low-cost treatments are available but there is a treatment gap of over 75% in many low- and middle-income countries. Investing in mental health is important for several reasons: the burden of mental illness is huge and costs societies enormous amounts, mental health is essential for economic development, and some interventions have been shown to be highly cost-effective "best buys" that can reduce future health costs. Without adequate investment in mental health services and supports, individuals and societies cannot reach their full potential.