This chapter presents the important concepts underlying the system dynamics modeling method. Following an initial definition of the term model, a summary of a successful system dynamics intervention is described. The key concepts of system dynamics – stocks and flows – are explained. The process for simulating stock and flow models – integral calculus – is described, with an example of a company’s customer base used to illustrate how stocks change, through their flows, over time. A summary of dimensional analysis for stock and flow equations is provided before the second feature of system dynamics modeling – feedback – is presented. The chapter concludes by summarizing the system dynamics meth-odology, which is a five-stage iterative process that guides model design, devel-opment, test and policy design.