In this book, the main principles involved in the design of this range of models are articulated, providing an account of the current state of the art as well as future research challenges. Topics covered include the Lowry model, the retail model, principles of account-based models and the methods rooted in Boltzmann-style statistical modelling and the Lotka-Volterra approach to system evolution. Applications range from urban and regional planning to wars and epidemics.