This paper deals with two aspects concerning the optimization of municipal solid waste combustion MSWC processes. First of all, an on-line calorific value sensor is discussed by means of which the calorific value of the waste can be estimated from actual process data. Experimental results on a MSWC process are discussed which show that the sensor performs well. By means of a proper integration in the control system of an MSW combustion process a significant improvement of the control performance is expected. The second aspect is the validation of dynamic first-principles models in general and of a dynamic first-principles model of the MSW combustion process in particular on the basis of actual process data. A validated model is a powerful tool for optimization of the process operation performance. A validated dynamic model is particularly useful for the optimization of the control system of a process. A validation method is proposed using so-called system identification techniques. The proposed method was found to be a powerful tool for the validation of the MSWC first-principles model. This model was used to develop and test a new control concept for the MSWC process. It is shown that the control performance of a MSWC process can be improved significantly by this new control concept.