Between 1990 and 2013, the number of people suffering from depression and/or anxiety increased by nearly 50%, from 416 million to 615 million. Despite its enormous health, social and economic burden, mental disorders continue to be driven into the shadows by stigma, prejudice and fear. Yet, according to a new WHO-led study, every US$ 1 invested in scaling up treatment for depression and anxiety leads to a return of US$ 4 in better health and ability to work.