Ed Diener, J. R. Smiley Professor of Psychology at the University of Illinois, is the world's foremost authority on the science of happiness. His son, Robert Biswas-Diener is a life coach and has been called ''the Indiana Jones of psychology'' because of his data collection adventures around the world. In this fascinating book the father and son team presents scientific evidence revealing that happiness is not overrated, and is good for people's health, social relationships, job success, longevity, and altruism. Happy people even tend to earn higher incomes. But people can be too happy for maximum success, and the pursuit of ultra-happiness can be detrimental. They advocate an optimal level of happiness in which people do not seek euphoria, but pursue life satisfaction, meaning, and frequent positive emotions, with recognition that some negative emotions are an integral part of a happy life. The authors describe why happiness alone is not enough; people need to be happy for the right reasons. They describe the new concept of Psychological Wealth, which extends beyond material riches, and beyond popular concepts like emotional intelligence and social capital.

The authors describe the evidence on what causes happiness. Although there are genetic influences on happiness, these genetics do not produce an unchanging happiness ''set-point.'' The book describes the authors' data collection around the globe that shows that people are not necessarily ''born'' happy, but can and do change their levels of happiness.

This book reveals that high income is correlated with happiness, although excessive materialism is toxic to it. The important factor is not so much what one can buy with one's income, but one's attitudes to it. Diener and Biswas-Diener also show that although religious people on average often are happier, not all religions are equal in this respect. They suggest that positive emotional spirituality - feeling positive emotions such as love and gratitude that connect people with things larger than themselves - is a major ingredient of happiness.

The authors provide a model for a happy approach to life, based on Attention, Interpretation, and Memory (AIM). They also review the happiness forecasting errors people make in forming decisions about future happiness, and offer some ways to avoid those errors. Diener and Biswas-Diener suggest that happiness is about a way of traveling, learning to react in positive ways to the world, rather than simply being a destination or set of circumstances.