The modelling of air flows to investigate indoor air quality and energy issues has been a topic at the AIVC for all of its 40 years. Models have been developed that range in complexity from single-zone algebraic expressions that can be calculated by hand to complex multi-zone approaches that integrate contaminant transport and other functions. Key advancements have come in terms of increased computer speed and storage capabilities, (leading to more complex multi-zone approaches and smaller time-step/longer simulation periods), improved used interfaces, and better input data (e.g., wind pressure coefficients).