Julian Simon made fundamental contributions to the literature on population economics between the mid-1970s and his premature death in 1998. His ideas were controversial, often extremely so. Even more than Esther Boserup, Simon became practically a cult figure, symbolizing the argument that population growth has propitious effects on economic growth. He repeated this argument in paper after paper, and book after book, contradicting the doomsayers and the neo-Malthusians. He emphasized the obvious, but frequently glossed-over, fact that human capital has to be embodied in human beings; thus the more people born, the more human capital there will be, and the higher will be the probability of significant new knowledge being created, the more scientists there will be, and the faster will be the pace of technological change. Simply put: people are “the primary causal variable” (p. 15) in economic growth.