System Dynamics is our adaptation of the input-output model used in economics to depict the interaction of sectors in an economy. While a quantitative technique used by many (including Wassily Leontief, winning him a Nobel Price in Economics), the method presented in this chapter speaks to local perspectives on complex systems. It helps people explore how they define and understand differences between parts of a system (e.g. causal factors or programme activities), how parts interact with each other and how they relate to the whole. It promotes holistic thinking that is also local. System Dynamics also invites participants to act based on their analysis of potential entry points into a system that offers opportunities for new learning and social change. These system entry points may be where change needs to happen the most, where change is most effective and easiest to accomplish, or where new understanding challenges people to rethink existing behaviour.