This book presents a new law of human behavior founded by the author some twenty-five years ago, but not proclaimed as a law until now. The Law of Escalating Marginal Sacrifice (LEMS) states that when a person exerts more effort pursuing a job, task, or goal, the negative outcomes, or costs experienced by the person as a result of the higher effort exerted, rise at an increasing rate_the rate of increase accelerating rapidly as one's effort capacity is approached. Such a relationship, between effort exerted and perceived costs associated with that effort, has profound implications for managing people in the workforce. This relationship provides a vital framework for integrating the theory of the firm with the theory of individual behavior_a synthesis too long neglected.