Jonathan Saunders for TIME University of Illinois professor Edward Diener has been sizing up life satisfaction for 25 years. His wife and a son, both psychologists, are occasional collaborators

Sugary white sand gleams under the bright yucatan sun, aquamarine water teems with tropical fish and lazy sea turtles, cold Mexican beer beckons beneath the shady thatch of palapasit's hard to imagine a sweeter spot than Akumal, Mexico, to contemplate the joys of being alive. And that was precisely the agenda when three leading psychologists gathered in this Mexican paradise to plot a new direction for psychology.

For most of its history, psychology had concerned itself with all that ails the human mind: anxiety, depression, neurosis, obsessions, paranoia, delusions. The goal of practitioners was to bring patients from a negative, ailing state to a neutral normal, or, as University of Pennsylvania psychologist Martin Seligman puts it, "from a minus five to a zero." It was Seligman who had summoned the others to Akumal that New Year's Day in 1998his first day as president of the American Psychological Association (A.P.A.)to share a vision of a new goal for psychology. "I realized that my profession was half-baked. It wasn't enough for us to nullify disabling conditions and get to zero. We needed to ask, What are the enabling conditions that make human beings flourish? How do we get from zero to plus five?"

Every incoming A.P.A. president is asked to choose a theme for his or her yearlong term in office. Seligman was thinking big. He wanted to persuade substantial numbers in the profession to explore the region north of zero, to look at what actively made people feel fulfilled, engaged and meaningfully happy. Mental health, he reasoned, should be more than the absence of mental illness. It should be something akin to a vibrant and muscular fitness of the human mind and spirit.

Over the decades, a few psychological researchers had ventured out of the dark realm of mental illness into the sunny land of the mentally hale and hearty. Some of Seligman's own research, for instance, had focused on optimism, a trait shown to be associated with good physical health, less depression and mental illness, longer life and, yes, greater happiness. Perhaps the most eager explorer of this terrain was University of Illinois psychologist Edward Diener, a.k.a. Dr. Happiness. For more than two decades, basically ever since he got tenure and could risk entering an unfashionable field, Diener had been examining what does and does not make people feel satisfied with life. Seligman's goal was to shine a light on such work and encourage much, much more of it.

To help him realize his vision, Seligman invited Ray Fowler, then the long-reigning and influential CEO of the A.P.A., to join him in Akumal. He also invited Hungarian-born psychologist Mihaly Csikszentmihalyi (pronounced cheeks sent me high), best known for exploring a happy state of mind called flow, the feeling of complete engagement in a creative or playful activity familiar to athletes, musicians, video-game enthusiastsalmost anyone who loses himself in a favorite pursuit. By the end of their week at the beach, the three had plans for the first-ever conference on positive psychology, to be held in Akumal a year laterit was to become an annual eventand a strategy for recruiting young talent to the nascent field. Within a few months, Seligman, who has a talent for popularizing and promoting his areas of interest, was approached by the Templeton Foundation in England, which proceeded to create lucrative awards for research in positive psych. The result: an explosion of research on happiness, optimism, positive emotions and healthy character traits. Seldom has an academic field been brought so quickly and deliberately to life.

What Makes Us Happy

So, what has science learned about what makes the human heart sing? More than one might imaginealong with some surprising things about what doesn't ring our inner chimes. Take wealth, for instance, and all the delightful things that money can buy. Research by Diener, among others, has shown that once your basic needs are met, additional income does little to raise your sense of satisfaction with life. A good education? Sorry, Mom and Dad, neither education nor, for that matter, a high IQ paves the road to happiness. Youth? No, again. In fact, older people are more consistently satisfied with their lives than the young. And they're less prone to dark moods: a recent survey by the Centers for Disease Control and Prevention found that people ages 20 to 24 are sad for an average of 3.4 days a month, as opposed to just 2.3 days for people ages 65 to 74. Marriage? A complicated picture: married people are generally happier than singles, but that may be because they were happier to begin with. Sunny days? Nope, although a 1998 study showed that Midwesterners think folks living in balmy California are happier and that Californians incorrectly believe this about themselves too.

On the positive side, religious faith seems to genuinely lift the spirit, though it's tough to tell whether it's the God part or the community aspect that does the heavy lifting. Friends? A giant yes. A 2002 study conducted at the University of Illinois by Diener and Seligman found that the most salient characteristics shared by the 10% of students with the highest levels of happiness and the fewest signs of depression were their strong ties to friends and family and commitment to spending time with them. "Word needs to be spread," concludes Diener. "It is important to work on social skills, close interpersonal ties and social support in order to be happy."