With new legislation and federal regulation for vehicle emission levels, automotive and truck manufacturers have been prompted to focus on emission control technologies that limit the level of exhaust pollutants. One of the primary pollutants, especially from diesel engines, is oxides of nitrogen (NOx). One possible solution to this pollution challenge is to design a more efficient internal combustion engine, which would require better engine operating parameter controls. However, there are limitations associated with such tight engine management. This need has led researchers and engineers to focus on the development of exhaust aftertreatment devices that will reduce NOx emissions with current diesel engines. An optimum aftertreatment device must be unaffected by exhaust-gas impurity poisoning such as sulfur products, and must have minimal impact on vehicle operations and fuel economy. One promising technology for NOx control is a non-thermal plasma (NTP) and catalyst system, which is a two-stage process that is comprised of a plasma-assisted catalyst that reduces nitric oxide (NO) and nitrogen dioxide (NO₂) emissions. The plasma portion of the system is used to oxidize nitric oxide (NO) present in the exhaust stream to nitrogen dioxide (NO₂). The nitrogen dioxide is then reduced to nitrogen (N₂) in a selective catalytic reduction (SCR) process, using the hydrocarbons present in the exhaust stream as the reductant. This paper presents an overview of a non-thermal plasma assisted catalyst system as applied to a small displacement diesel powered vehicle. In addition to effectively reducing NOx emissions, it has been found that a non-thermal plasma can also destroy a portion of the particulate matter (PM) that is emitted from diesel engines. Delphi Automotive Systems in conjunction with Pacific Northwest National Laboratories has been developing such an exhaust aftertreatment system to reduce emissions form diesel vehicles. The results of testing and system evaluation is discussed in general, and the effectiveness on reducing oxides of nitrogen and particulate matter emissions from diesel vehicles is presented.