Everyone, it seems—from Buddhist monks to positive psychologists, from Charles Schulz to the Beatles—has offered opinions on what it means to be happy. And whether you believe that bliss is found with a warm puppy or a warm gun, in a Prozac prescription or the pages of self–help books, you likely crave more of it. For all the bumper–sticker clichés and pop–culture platitudes, though, happiness is one of the less–studied human emotions. It’s not a “treatable” problem like sadness, anger, or fear, and its very essence seems more the stuff of greeting cards than hard science. That’s changing, however, as a growing number of researchers—including several affiliated with Harvard Medical School—are uncovering surprising facts about the nature of delight.