Steady state kinetics data from a commercial Pt-based lean NOx catalyst have been used to formulate a kinetic model to describe the performance of the catalyst. Tt is clear from this analysis that steady state kinetics in isolation are not sufficient to provide a full picture of the operational performance of such a catalyst. However, when this kinetic analysis is combined with mechanistic information obtained over the catalyst, the resulting model is extremely powerful. Within this paper, the development of the kinetic model is described, and the requirement for both accurate mechanistic information and detailed kinetic measurements is clearly demonstrated. The use of the model to predict the performance of a light-duty diesel vehicle under light-off conditions is described, and the power and flexibility of the model, and indeed of the modelling approach within the lean NOx area, are emphasised.