Arguing that the ultimate resource is the human imagination coupled to the human spirit, Julian Simon has led a vigorous challenge to conventional beliefs about scarcity of energy and natural resources, pollution of the environment, the effects of immigration, and the "perils of overpopulation." The comprehensive data, careful quantitative research, and economic logic contained in the first edition of The Ultimate Resource rebutted widely held professional judgments about the threat of overpopulation. In Simon's view, the key factor in natural and world economic growth is our capacity for the creation of new ideas and contributions to knowledge. The more people alive who can be trained to help solve the problems that confront us, the faster we can remove obstacles, and the greater the economic inheritance we shall bequeath to our descendants. In conjunction with the size of the educated population, the key constraint on human progress is the nature of the economic-political system: Talented people need economic freedom and security to bring their talents to fruition.