Debates over what's important to happiness — Money? Children? Love? Achievement? — are ancient and universal, but attempts to study the subject empirically are much newer. What have psychologists learned about which factors have a strong effect on people's happiness and which don't? Are parents really less happy than non-parents, and do people return to their happiness "set point" even after extreme events like winning the lottery or becoming paralyzed? We also tackle some of the philosophical questions regarding happiness, such as whether some kinds of happiness are "better" than others, and whether people can be mistaken about their own happiness. But, perhaps the hardest question is: can happiness really be measured?