Fifteen years ago, on a mid-August day in San Francisco’s massive Moscone Center, thousands of psychologists sat entranced as one of their peers announced the birth of a new field of psychology. Their discipline had learned a great deal about what goes wrong in the human condition, said the speaker, but had up to this point virtually ignored the question of what goes right. That was about to change.

The speaker was Martin Seligman, president of the American Psychological Association, and he was addressing the APA’s annual convention, announcing an incredibly ambitious new effort he described as a “Manhattan Project for the social sciences”—a positive psychology. In layman’s terms, a science of happiness.

A decade and a half later, the field of positive psychology has produced an avalanche of new research. Institutions from school systems to the U.S. military have implemented its findings, Fortune 500 corporations hire happiness consultants, and hardly a week goes by without some new book on happiness topping the New York Times bestseller list.

And this is no mere fad. Last year the Harvard Business Review dedicated its January issue to the topic. “We’ve learned a lot about how to make people happy,” declared the editors. “We’d be stupid not to use that knowledge.”

So what is that knowledge? Exactly what have we learned in the past fifteen years?

First, that happiness is available. Our level of happiness (much like our brains and nerve pathways, as the neuroscientists have learned over the same period) is far more malleable than we thought. We are not so hardwired—by genetics, upbringing, or past experience—to a fixed range of mood state as science insisted was the case just twenty years ago.

What’s more, the factors that can make us significantly and lastingly happier are not the big things we might expect would make the difference, but the little things we so easily overlook. A consistently positive outlook. Expressing gratitude regularly. A habit of savoring little things in the moment. Simple acts of kindness and generosity to others. Greater investment in friendships and engagement in meaningful activities.

And the most radical finding of all: success does not lead to greater happiness—it’s the other way around.

People who have higher levels of happiness, the scientists are telling us, also perform better at work, have more successful careers, and earn more; are more resistant to everything from colds and viruses to stroke and heart attack; have better and longer-lasting marriages and more satisfying friendships; are more involved in their communities; and live longer.

Doing the things that make you happier don’t just make you happier.

They also make your life—and business—work better.

JOHN DAVID MANN is Consulting Editor of Networking Times.