The results of a development program for three-way Catalysts with improved thermal Stability targeting at the future emission control standards for passenger cars are reported. The influence of newly developed washcoat ingredients on catalyst performance is demonstrated by model gas and engine tests, and the most promising systems were evaluated on different vehicles in U.S. and E.U. driving cycles. The study concentrated mainly on Pd/Rh-based catalysts, which are able to meet Phase III 1997 legislation. The advantages of the new catalysts reported are mainly found in an improved dynamic conversion especially for NOx.