Welcome to the frenzy, now peaking at a Barnes & Noble near you: In 2008 4,000 books were published on happiness, while a mere 50 books on the topic were released in 2000. The most popular class at Harvard University is about , and at least 100 other universities offer similar courses. Happiness workshops for the post-collegiate set abound, and each day "life coaches" promising bliss to potential clients hang out their shingles.

In the late 1990s, psychologist of the University of Pennsylvania exhorted colleagues to scrutinize optimal moods with the same intensity with which they had for so long studied pathologies: We'd never learn about full human functioning unless we knew as much about mental wellness as we do about mental illness. A new generation of psychologists built up a respectable body of research on positive character traits and happiness-boosting practices. At the same time, developments in neuroscience provided new clues to what makes us happy and what that looks like in the brain. Not to be outdone, behavioral economists piled on research subverting the classical premise that people always make rational choices that increase their well-being. We're lousy at predicting what makes us happy, they found.

It wasn't enough that an array of academic strands came together, sparking a slew of insights into the sunny side of life. Self-appointed experts jumped on the happiness bandwagon. A shallow sea of yellow smiley faces, gurus, and purveyors of kitchen-table have strip-mined the science, extracted a lot of fool's gold, and stormed the marketplace with guarantees to annihilate your worry, stress, anguish, dejection, and even ennui. Once and for all! All it takes is a little . Or maybe a lot.

But all is not necessarily well. According to some measures, as a nation we've grown sadder and more during the same years that the happiness movement has flourished; perhaps that's why we've eagerly bought up its offerings. It may be that college students sign up for positive psychology lessons in droves because a full 15 percent of them report being clinically depressed.

There are those who see in the happiness brigade a glib and even dispiriting Pollyanna gloss. So it's not surprising that the happiness movement has unleashed a counterforce, led by a troika of academics. Jerome Wakefield of New York University and Allan Horwitz of Rutgers have penned The Loss of Sadness: How Transformed Normal Sorrow into Depressive Disorder, and Wake Forest University's Eric Wilson has written a defense of melancholy in Against Happiness. They observe that our preoccupation with happiness has come at the cost of sadness, an important feeling that we've tried to banish from our emotional repertoire.

Horwitz laments that young people who are naturally weepy after breakups are often urged to medicate themselves instead of working through their sadness. Wilson fumes that our obsession with happiness amounts to a "craven disregard" for the melancholic perspective that has given rise to our greatest works of art. "The happy man," he writes, "is a hollow man."

Both the happiness and anti-happiness forces actually agree on something important—that we Americans tend to grab superficial quick fixes such as extravagant purchases and fatty foods to subdue any negative feelings that overcome us. Such measures seem to hinge on a belief that constant happiness is somehow our birthright. Indeed, a body of research shows instant indulgences do calm us down—for a few moments. But they leave us poorer, physically unhealthy, and generally more miserable in the long run—and lacking in the real skills to get us out of our rut.

Happiness is not about smiling all of the time. It's not about eliminating bad moods, or trading your Tolstoy-inspired nuance and ambivalence toward people and situations for cheery pronouncements devoid of critical judgment. While the veritable experts lie in different camps and sometimes challenge one another, over the past decade they've together assembled big chunks of the happiness puzzle.

What is happiness? The most useful definition—and it's one agreed upon by neuroscientists, psychiatrists, behavioral economists, positive psychologists, and Buddhist monks—is more like satisfied or content than "happy" in its strict bursting-with-glee sense. It has depth and deliberation to it. It encompasses living a meaningful life, utilizing your gifts and your time, living with thought and purpose.

It's maximized when you also feel part of a community. And when you confront annoyances and crises with grace. It involves a willingness to learn and stretch and grow, which sometimes involves discomfort. It requires acting on life, not merely taking it in. It's not joy, a temporary exhilaration, or even pleasure, that sensual rush—though a steady supply of those feelings course through those who seize each day.

There has been real progress in understanding happiness and how to get it. Here are the greatest hits, as it were, that jump out from the research.

Some People Are Born Happy

Some lucky souls really are born with brighter outlooks than others; they simply see beauty and opportunity where others hone in on flaws and dangers. But those with a more ominous orientation can alter their outlook, at least to a point. They can learn to internally challenge their fearful thoughts and negative assumptions—"she thinks I'm an idiot," "I'm going to get fired," "I'll never be a good mom"—if not eliminate them altogether. Engaging in positive internal dialogue is actually a mark of the mentally healthy.

Getting What You Want Doesn't Bring Lasting Happiness

You think happiness would arrive if you were to win the lottery, or would forever fade away if your home were destroyed in a flood. But human beings are remarkably adaptable. After a variable period of adjustment, we bounce back to our previous level of happiness, no matter what happens to us. (There are some scientifically proven exceptions, notably suffering the unexpected loss of a job or the loss of a spouse. Both events tend to permanently knock people down a notch.)

Our adaptability works in two directions. Because we are so adaptable, points out Sonja Lyubomirsky, a professor of psychology at the University of California, Riverside, we quickly get used to many of the accomplishments we strive for in life, such as landing the big job or getting married. Soon after we reach a milestone, we start to feel that something is missing. We begin coveting another worldly possession or eyeing a social advancement. But such an approach keeps us tethered to the " ," where happiness is always just out of reach, one toy or one notch away. It's possible to get off the treadmill entirely, Lyubomirsky says, by focusing on activities that are dynamic, surprising, and -absorbing, and thus less likely to bore us than, say, acquiring shiny stuff.

Pain Is a Part of Happiness

Happiness is not your reward for escaping pain. It demands that you confront negative feelings head-on, without letting them overwhelm you. Russ Harris, a medical doctor-cum-counselor and author of The Happiness Trap, calls popular conceptions of happiness dangerous because they set people up for a "struggle against reality." They don't acknowledge that real life is full of disappointments, loss, and inconveniences. "If you're going to live a rich and meaningful life," Harris says, "you're going to feel a full range of emotions."

The point isn't to limit that palette of feelings. After all, negative states cue us into what we value and what we need to change: for a loved one proves how much we cherish our relationships. Frustration with several jobs in a row is a sign we're in the wrong . Happiness would be meaningless if not for sadness: Without the contrast of darkness, there is no light.

Mindfulness Brings Happiness

, a mental state of relaxed awareness of the present moment, marked by and curiosity toward your feelings rather than judgments of them, is a powerful tool for experiencing happiness when practiced regularly. "If you bring mindfulness to bear on negative feelings, they lose their impact. Just let them be there without struggling against them, and you'll eventually feel less anxiety and ," Harris says. Don't banish your negative feelings, but don't let them get in the way of your taking productive actions, either.

Happiness Lies in the Chase

Action toward other than happiness makes us happy. Though there is a place for vegging out and reading trashy novels, easy pleasures will never light us up the way mastering a new skill or building something from scratch will.

And it's not crossing the finish line that is most rewarding; it's anticipating achieving your goal. University of Wisconsin Richard Davidson has found that working hard toward a goal, and making progress to the point of expecting a goal to be realized, doesn't just activate positive feelings—it also suppresses negative emotions such as and depression.

Yes, Money Buys Happiness—At Least Some Money and Some Happiness

Money does buy happiness, but only up to the point where it enables you to live comfortably. Beyond that, more cash doesn't boost your well-being. But brings true joy, so striking it rich could in fact underwrite your happiness—if you were to give your wealth away.

Happiness Is Relative

Whether or not we are keeping up with the Joneses—a nagging thought known as status anxiety—affects how happy we are. Some are more obsessed with status than others, but we're all attuned to how we're doing in life relative to those around us. To stop status worries from gnawing at your happiness, choose your peer group carefully. Owning the smallest mansion in a gated community could make you feel worse off than buying the biggest bungalow in a less affluent neighborhood.

Options Make Us Miserable

We're constantly making decisions, ranging from what to eat for dinner each night to whom we should marry, not to mention all those flavors of ice cream. We base many of our decisions on whether we think a particular preference will increase our well-being. Intuitively, we seem convinced that the more choices we have, the better off we'll ultimately be. But our world of unlimited opportunity imprisons us more than it makes us happy. In what Swarthmore psychologist Barry Schwartz calls "the paradox of choice," facing many possibilities leaves us out—and less satisfied with whatever we do decide. Having too many choices keeps us wondering about all the opportunities missed.

Happiness Is Other People

Positive psychologist Chris Peterson, a professor at the University of Michigan, says the best piece of advice to come out of his field is to make strong personal relationships your priority. Good relationships are buffers against the damaging effects of all of life's inevitable letdowns and setbacks.

Do Your Happiness Homework

You can increase positive feelings by incorporating a few proven practices into your routine. Lyubomirsky suggests you express your gratitude toward someone in a letter or in a weekly journal, visualize the best possible future for yourself once a week, and perform acts of kindness for others on a regular basis to lift your mood in the moment and over time. "Becoming happier takes work, but it may be the most rewarding and fun work you'll ever do," she says.

Happiness Hinges on Your Time Frame

Feeling happy while you carry out your day-to-day activities may not have much to do with how satisfied you feel in general. Time skews our perceptions of happiness. Parents look back warmly on their children's preschool years, for example. But Daniel Kahneman of Princeton University found that childcare tasks rank very low on the list of what makes people happy, below napping and watching TV. And yet, if you were to step back and evaluate a decade of your life, would a spirited stretch of raising children or a steady stream of dozing off on the couch each day in between soap operas illustrate a "happier" time? Evaluate your well-being at the macro as well as the micro level to get the most accurate picture of your own happiness.

You're Wrong About What Will Make You Happy and You're Wrong About What Made You Happy

Harvard psychologist Daniel Gilbert discovered a deep truth about happiness: Things are almost never as bad—or as good—as we expect them to be. Your promotion will be quite nice, but it won't be a 24-hour parade. Your breakup will be very hard, but also instructive, and maybe even energizing. We are terrible at predicting our future feelings accurately, especially if our predictions are based on our past experiences. The past exists in our , after all, and memory is not a reliable recording device: We recall beginnings and endings far more intensely than those long "middles," whether they're eventful or not. So the horrible beginning of your vacation will lead you astray in deciding the best place to go next year.

Gilbert's take-away advice is to forgo your own mental projections. The best predictor of whether you'll enjoy something is whether someone else enjoyed it. So simply ask your friend who went to Mexico if you, too, should go there on vacation.

Happiness Is Embracing Your Natural Coping Style

Not everyone can put on a happy face. Barbara Held, a professor of psychology at Bowdoin College, for one, rails against "the tyranny of the positive attitude." "Looking on the bright side isn't possible for some people and is even counterproductive," she insists. "When you put pressure on people to cope in a way that doesn't fit them, it not only doesn't work, it makes them feel like a failure on top of already feeling bad."

The one-size-fits-all approach to managing emotional life is misguided, agrees Julie Norem, author of The Positive Power of . In her research, the Wellesley professor of psychology has shown that the defensive pessimism that anxious people feel can be harnessed to help them get things done, which in turn makes them happier. A naturally pessimistic architect, for example, can set low expectations for an upcoming presentation and review all of the bad outcomes that she's imagining, so that she can prepare carefully and increase her chances of success.

Happiness Is Living Your Values

If you aren't living according to your values, you won't be happy, no matter how much you are achieving. Some people, however, aren't even sure what their values are. If you're one of them, Harris has a great question for you: "Imagine I could wave a magic wand to ensure that you would have the approval and admiration of everyone on the planet, forever. What, in that case, would you choose to do with your life?"

Once you've answered honestly, you can start taking steps toward your ideal vision of yourself. You can tape positive affirmations to your mirror, or you can cut up your advice books and turn them into a papier-mâché project. It doesn't matter, as long as you're living consciously. The state of happiness is not really a state at all. It's an ongoing personal experiment.