Mihaly Csikszentmihalyi's Flow has achieved such an iconic status that people use the concept regularly, often, one might presume, without knowledge of the research and insight that went into its creation. It comes from the 1980s, a time when budding neuroscience and an ever-eager drive to redefine psychology and learning spawned new interest in humanity's finer points, among them, the search for happiness. It's an important book for these reasons. It also struggles to hold up to the piles of new research that Csikszentmihalyi, and others in his era, helped to inspire. The core concept (spoiler alert), that Flow occurs when "skills" and "challenges" are essentially balanced, seems lithe and crisp at first. As Csikszentmihalyi attempts to support its application as a way to explain human happiness, the argument breaks down. The preponderance of human-interest stories that make up most of the book are interesting, though, function more as a means of establishing the reality that people the world over are happy for different reasons than as a support for his premise. As a launching point for others, however Csikszentmihalyi does create an outline of meaningful questions for us to ask about human happiness, an area of research that has become as respected and essential in the psychological community as it is influential on the day-to-day life of people outside the sciences.