In the last twenty years injection molding and blow molding have seen a rapid growth due to the development of new application areas in the automotive, sports and leisure, electronics, transportation and packaging industries. This success can be traced to the optimization of existing processes and to the development of new processing techniques employing novel concepts such as gas-assisted injection molding, co-injection, and 3D and sequential blow molding. The complexity of these new molding techniques calls for a much better understanding of the material behavior during the basic stages of the process and its relation to the properties and performance of the final part. These characteristics are directly dependent upon die and mold designs and on the operating conditions during extrusion, injection, inflation and cooling in the mold.In this paper we will demonstrate how the numerical simulation of the individual steps of the process can be used to optimize the process and product performance of industrial parts. In the case of injection molding, special interest will be devoted to the numerical prediction of the filling phase for both thin and thick parts. For blow molding the prediction of material behavior during clamping and inflation will be shown and related to final part thickness distribution, parison programming and preform design.