This paper represents an overview of some basic issues faced by the diesel engine designer looking to the 1990's. Current (medium duty truck engine) technology with some enhancements can be used to “achieve” 1991 emissions. However, the substantially lower goals required for production variability and deterioration factor require more innovative approaches and a reduction in fuel sulfur. Important considerations for selecting 1990's fuel injection system, combustion chamber geometry, and charge air approach are discussed based on substantial testing. It is concluded there are a variety of 1990's choices requiring each manufacturer to consider their market, company goals and competitive pressures.