Good building performance is contingent on complex, interacting factors. The application of performance simulation tools allows practitioners to adopt a virtual prototype and test approach in selecting design solutions that balance performance and cost. The aim of this book is to provide guidance on approaches to the modelling and simulation of energy systems in the built environment at various scales and complexities to address the myriad challenges of the clean energy transition. The intention is to equip the reader with the understanding required to compose high integrity models, commission realistic simulations, and interpret predictions to assess life cycle performance and ensure operational resilience. Initial chapters introduce the impressive capabilities of building energy systems simulation and the new features that are likely to be added in future. The authors then describe the sustainable energy challenge and how modelling and simulation can be used to scrutinise proposals in a cost-effectively manner. The remainder of the book then covers different technology options including electrification of heating, net zero energy housing, community energy systems, active demand management, and urban energy action planning. In each case the nature of the problem is described, the construction of a high-fidelity computer model elaborated, and principal simulation outcomes demonstrated. Some of the problem domains addressed in the book are accompanied by a high-fidelity digital model available externally. These models are compatible with the ESP-r performance simulation program, which is freely available under an open-source licence. Applied Building Performance Simulation provides a thorough grounding and practical guidance in the role of software simulation tools for building performance, for an audience of researchers, industry professionals, advanced students, and policy makers, regulators and standards bodies operating in the field.