Could you make yourself happier?
20 June 2013 Last updated at 09:22 BST
Depression has become the biggest cause of disability on the planet, according to the World Health Organisation.
Psychologists say everyone could do more to improve mental health and become happier.
The World Database of Happiness Studies in the Netherlands collates the findings on research into the subject, and has made some surprising discoveries.
Pascale Harter reports.