Sages going back to Socrates have offered advice on how to be happy, but only now are scientists beginning to address this question with systematic, controlled research. Although many of the new studies reaffirm time-honored wisdom ("Do what you love," "To thine own self be true"), they also add a number of fresh twists and insights. We canvassed the leading experts on what happy people have in common—and why it's worth trying to become one of them:

They find their most golden self. Picture happiness. What do you see? A peaceful soul sitting in a field of daisies appreciating the moment? That kind of passive, pleasure-oriented—hedonic—contentment is definitely a component of overall happiness. But researchers now believe that eudaimonic well-being may be more important. Cobbled from the Greek eu ("good") and daimon ("spirit" or "deity"), eudaimonia means striving toward excellence based on one's unique talents and potential—Aristotle considered it to be the noblest goal in life. In his time, the Greeks believed that each child was blessed at birth with a personal daimon embodying the highest possible expression of his or her nature. One way they envisioned the daimon was as a golden figurine that would be revealed by cracking away an outer layer of cheap pottery (the person's baser exterior). The effort to know and realize one's most golden self—"personal growth," in today's lingo—is now the central concept of eudaimonia, which has also come to include continually taking on new challenges and fulfilling one's sense of purpose in life.

"Eudaimonic well-being is much more robust and satisfying than hedonic happiness, and it engages different parts of the brain," says Richard J. Davidson, PhD, of the University of Wisconsin-Madison. "The positive emotion accompanying thoughts that are directed toward meaningful goals is one of the most enduring components of well-being." Eudaimonia is also good for the body. Women who scored high on psychological tests for it (they were purposefully engaged in life, pursued self-development) weighed less, slept better, and had fewer stress hormones and markers for heart disease than others—including those reporting hedonic happiness—according to a study led by Carol Ryff, PhD, a professor of psychology at the University of Wisconsin-Madison.