The prosperity of modern society is unthinkable without technology. One of the most important technical products so far is undoubtedly the automobile. It has been used by man to satisfy his deeprooted desire for freedom, independence and mobility.500 million motor vehicles on the roads across the world are clear evidence of the fact that society no longer wants to forego the benefit of the automobile.According to the forecasts of several experts, the car population may reach 1.3 billion by the middle of the next century - if the markets keep developing as expected.This enormous growth rate places an obligation on engineers in the automobile industry to do everything to further improve the automobile.Above all, this demands an additional deduction of fuel consumption as well as efforts to keep negative impact on the environment to a minimum.Modern high speed direct injection diesel engines distinguish themselves from other internal combustion engines through their high efficiency. This efficiency contributes significantly to the management of available crude oil reserves. Moreover, two further consequences of their low consumption are of increasing interest:Firstly, there is the opportunity for a positive effect on the balance of foreign trade.Secondly, and no less important, there is the opportunity to reduce the atmospheric burden of CO2 emissions.Given that environmentally responsible, i.e. thrifty and more sustainable, consumption is becoming increasingly important to the human conscience worldwide, the automotive industry's ability to deliver the appropriate technology is currently very much in demand. A few years ago, only limited improvements in diesel fuel economy seemed plausible.However, in the meantime intensive developments in the fields of fuel injection, supercharging and materials have opened up the potential for fuel consumption improvement to a practicable level of 3 litres per 100km (78 miles per US gallon, 94 miles per UK gallon) with lightweight cars.Such improvements cannot simply be achieved through engine modification.Future success will depend on how well-coordinated and focussed, the collaborators work together in vehicle development.According to recent investigations at AVL, it seems plausible that improvements beyond the previously mentioned fuel consumption level could be achieved through attention to the total drivetrain system, specifically through optimisation of friction parameters, rapid engine warm-up strategies and gear change strategies.Nevertheless, the conflict between achievement of pollutant emission limits and the minimisation of fuel consumption and noise remains, albeit against a background of the availability to engineers of new and highly advanced development tools.This paper deals principally with those technologies and methods which offer the best possible fuel economy, whilst still keeping the ever tighter emission and noise standards in mind. And some space is being reserved for exhaust gas aftertreatment technology.The paper would be incomplete without some discussion of the links between engine and vehicle fuel economy.