This course offers a comprehensive overview and practical exposure to energy system modelling for buildings and cities, emphasizing the significance of energy systems in contemporary infrastructure and their role in ensuring resilient, efficient, and sustainable civil engineering practices. The lectures will delve into fundamental physical concepts, mathematical principles, and software tools necessary for modelling energy systems in the context of cities and buildings. The theoretical aspects of the course will encompass foundational knowledge in heat transfer and building thermal dynamics. In parallel, the practical component of the course will introduce participants to an emerging equation-based programming language, utilizing Modelica as an illustrative example.