Application of various motor vehicle emission control technologies has established a history of success. This success, however, has largely been offset by the constantly growing numbers of vehicles and miles traveled. Heavy-duty diesel engine manufacturers have developed new technologies in response to increasingly stringent emission standards. The diesel engine has long been a champion of fuel economy, with advantages in reliability and durability over other power plants. Yet, controlling NOx, and particulate emissions has been a formidable challenge to the diesel industry because most traditional NOx, control approaches tend to increase particulate emissions, and vice versa.Despite this challenge, there is significant evidence that heavy-duty highway engine manufacturers can achieve substantial emission reductions. Many development programs carried out over the last five years have yielded remarkable results in laboratory demonstrations. The introduction of electronic controls to the heavy-duty diesel engine by industry has provided new opportunities for implementing even greater exhaust emission reductions while maintaining its fuel economy and durability advantages. Today, heavy-duty diesel engines exhibit excellent smoke control characteristics, which enable them to comply with very low particulate emission standards and essentially render the smoke Federal Test Procedure redundant.This paper reviews some of the most recent technological advances that contribute to the new optimism regarding the future of the diesel engine. Special emphasis is also placed on the synergistic effect that some of these technologies produce to help diesel engine manufacturers overcome future emission and performance challenges.