Decisionmakers at every level unconsciously use mental models to choose among policies that will shape people’s future world. People’s world model was built specifically to investigate five major trends of global concern–accelerating industrialization, rapid population growth, widespread malnutrition, depletion of nonrenewable resources, and a deteriorating environment. Decisions are being made every day, in every part of the world, that will affect the physical, economic, and social conditions of the world system for decades to come. Growth will be stopped by pressures that are not of human choosing, and that, as the world model suggests, may be very much worse than those which society might choose for itself. Every day of continued exponential growth brings the world system closer to the ultimate limits to that growth. Man possesses, for a small moment in his history, the most powerful combination of knowledge, tools, and resources the world has ever known.