Major advances in TWC catalysis have been reported in the past several years. Possibly the most significant of these has been the development of high loaded Pd-only catalysts which demonstrate improved HC and light-off performance. Such systems have demonstrated the ability to meet California Low Emission Vehicle Standards without the need for electrically heated catalysts or hydrocarbon trap technology. The integration of improved low temperature catalyst performance with optimized catalyst substrate properties and vehicle calibration can result in further emission reductions.This paper describes the development of a low temperature Pt/Pd catalyst technology which offers light-off advantages over Pd-only catalysts. Mathematical modelling, combined with confirmation testing on an engine dynamometer and vehicles, demonstrate that further reductions in catalyst light-off and cold-start emissions can be achieved by combining this low temperature catalyst technology with low thermal mass substrates. The importance of vehicle calibration in affecting cold-start emissions is demonstrated by the realization that, with many present engine calibrations utilizing rich cold-start operation for the first 30-60 seconds, HC and CO light-off is often determined not by the catalyst technology, but by the time at which closed-loop stoichiometric control is achieved. By utilizing stoichiometric or lean cold-start strategies together with low thermal mass substrates, the improved low temperature performance of new catalyst technologies can be realized.