The European driving conditions and the demand for cars with high specific engine performance need a special design of the catalyst systems in view of geometry and materials. The experience with catalytic converters in the USA and Japan since more than 10 years forms the basis for application in Europe. The high level of thermal and mechanical stress requires a suitable design and the application of high quality materials for mounting system, housing, down pipe and exhaust manifold. Cross section and volume of the catalyst need to meet the higher exhaust flow. Additional to the wire mesh catalyst mounting system the heat expandable ceramic mat system is discussed too. Insulation of housing and down pipe by means of air gap and ceramic wool fleece are considered, especially in relation to the lower temperature level of the ECE-Test. Results of durability tests are presented. Cost for different designs are compared.