Using a system dynamics approach, this book illustrates the physics of fundamental accumulation processes (stocks and flows) across the demand and supply sectors of energy systems. Examples of system dynamics simulation models are presented where these accumulation processes are driving the behavior of the system. Based on these modeling efforts, two cases (the socio-economic and environmental implications of the energy policy of Pakistan and the dynamics of green power in Ontario, Canada) are analyzed and discussed. By studying the dynamics of the fundamental structures of an energy system, the reader gains an enhanced understanding of the stocks and flows of complex systems as well as their role in energy policy. This book is of use to managers and practitioners, teachers, researchers, and students of design and assessment of policy making for complex, dynamic energy systems.