In Human Action, Mises starts from the ideas set forth in his Theory and History that all actions and decisions are based on human needs, wants, and desires and continues deeper and further to explain how studying this human action is not only a legitimate science (praxeology) but how that science is based on the foundation of free-market economics. Mises presents and discusses all existing economic theories and then proceeds to explain how the only sensible, realistic, and feasible theory of economics is one based on how the needs and desires of human beings dictate trends, affect profits and losses, adjust supply and demand, set prices, and otherwise maintain, regulate, and control economic forces. Ludwig von Mises (1881-1973) was the leading spokesman of the Austrian School of economics throughout most of the twentieth century. Bettina Bien Greaves is a former resident scholar and trustee of the Foundation for Economic Education and was a senior staff member at FEE from 1951 to 1999.