Friday night's episode of 20/20 dedicated an hour to the new science of happiness—how it can be measured, studied, and nurtured. A number of positive psychologists shared their thoughts on the fundamentals of the search for happiness, among them Daniel Gilbert of Harvard University, the best-selling author of Stumbling on Happiness; Richard Davidson of the University of Wisconsin-Madison; and Sonja Lyubomirsky of the University of California-Riverside. The latest research is showing that happiness is within us—in what we do and how we think, every day of our lives—and that we can change our brains in positive ways. The people around us matter, too. Community counts in a big way, which why people are happy in Denmark (where they pay extremely high taxes) and Singapore (where rules are severely strict, there's one political party, and a censored press), and why one study found that people in the slums of Calcutta are happier than people living on the streets in California. —Heather Wax