Air quality models have become fundamental tools to analyze observations, understand relationships, test hypotheses, and project future evolution for air pollution. This course is aimed to provide insight into the methods used in air quality modelling. It will focus on both theory and practice, from the fundamental principles behind models to their applications in interpreting air pollution. Particular emphasis will be the mathematical methods for chemical and physical systems; steady-state dispersion models; Lagrangian transport models; indoor air quality models; chemical transport models; as well as model evaluation.