Everybody wants it. But what exactly is happiness? The pursuit of happiness has been recognized by everyone from poets to politicians as what makes the world go round. The world's largest and fastest-growing industries - alcohol, pharmaceuticals, mind altering drugs, self-help books, counselling, travel and tourism - all profit heavily from our intent to become completely happy with our lives. In the first comprehensive book to address this most basic of human desires, Daniel Nettle explores why we want to be happy, how we assess our levels of happiness, and the different ways that happiness is interpreted in different cultures. Using statistical information from the National Child Development Study, a project that has collected social and emotional data from thousands of people since 1958, Nettle shows the ways in which definitions and sources of happiness have changed over time.