Dispersion modelling is required for regulatory compliance demonstration, source performance assessment and design, environmental assessment, hazard risk assessment, and forensic evaluation. This diverse range of applications requires a range of different types of models, such as the regulatory models (AERMOD, ISCST3, Reg 346), Puff models such CALPUFF, denser than air models such as DEGADIS, and Grid models such as CMAQ and CAMx. We have been involved in the application of these and similar models for thousands of projects. Our knowledge of the meteorological data and numerical products allows us to assemble the meteorological files to drive the models. This expertise and facility with the model internals allows us to better understand the performance and shortcomings of the models to permit application in specialized settings or conditions, and to ensure that the results are demonstrable. CEMC has also developed rapidAER, a specialized modelling interface to AERMOD and a unique implementation of the AERMOD model which takes a fraction of the time to perform the extensive modelling required by regulations, and greatly facilitates the process of source configuration design.