Heavy-duty diesel engines are used in a wide variety of commercial vehicles. Recent changes in the emissions standards have lead to the use of catalytic exhaust aftertreatment in form of oxidation catalysts on diesel engines to reduce particulate emissions, If is expected that exhaust aftertreatment will continue to be used on diesel engines in order to meet future emissions standards. Diesel oxidation catalysts differ significantly from current passenger car gasoline catalysts in terms of the emissions reduced, the exhaust operating conditions, and the durability requirements. This paper discusses the development of a diesel catalyst in terms of engine emissions, operating conditions and durability requirements. Results on emissions performance of an engine/catalyst system and emissions durability of a diesel oxidation catalyst are presented to support the conclusions of this work.