Astute readers will note the influence of the Santa Fe Institute and concepts of "complex adaptive systems" in this book's title. Most social science models, including the general equilibrium model at the heart of modern neoclassical economics, mathematically reconstruct the aggregate behavior of populations by imposing highly simplified behavioral assumptions on them (for example, rational utility maximization). These models also tend to be static, that is, they cannot account for evolutionary change over time. Modeling "from the bottom up" means using computers to test the interaction of individual agents rather than aggregated populations, and has been used successfully in the life sciences to predict the evolution of complex biological systems. This book describes an extension of this methodology into the social sciences, in particular the authors' "sugarscape" society in which individual agents engage in sexual reproduction, trade, learning, and a range of social behaviors. While the issues raised here may seem overly technical for general readers, the use of this technique represents a recognition that existing models are too simplistic and mechanical ever to capture the realities of complex social systems. The next logical area for it to spread is into military modeling, and readers should expect further works along these lines in the coming years.