The use of modelling techniques for predicting the dispersion of odours from wastewater treatment plants is considered in relation to both the resolution of odour problems and the design requirements for new facilities. The issues of community odour annoyance and nuisance are discussed in the context of modelling averaging times, short-term odour peaks and the nature of the individual odours. In addition, the derivation of acceptable odour annoyance criteria is discussed with a comparison of different international approaches and a practical approach to resolving design criteria is proposed. Four case studies include the analysis and resolution of severe odour problems at two major wastewater treatment facilities and the evaluation of “Cordons Sanitaire” in the planning of new housing developments. In the first two cases, modelling was used to identify the most significant processes in terms of off-site effects and then to assess the required abatement level to achieve an acceptable complaints frequency. Inthe third case, dispersion modelling was used to assess the effectiveness of planned odour control measures in the release of land for residential development. The fourth case study demonstrates how an overly-stringent approach to odour control can cause problems.