Why do so few women occupy positions of power and prestige? Virginia Valian uses concepts and data from psychology, sociology, economics, and biology to explain the disparity in the professional advancement of men and women. According to Valian, men and women alike have implicit hypotheses about gender differences -- gender schemas -- that create small sex differences in characteristics, behaviors, perceptions, and evaluations of men and women. Those small imbalances accumulate to advantage men and disadvantage women. The most important consequence of gender schemas for professional life is that men tend to be overrated and women underrated. Valian's goal is to make the invisible factors that retard women's progress visible, so that fair treatment of men and women will be possible. The book makes its case with experimental and observational data from laboratory and field studies of children and adults, and with statistical documentation on men and women in the professions. The many anecdotal examples throughout provide a lively counterpoint.