The tightening of future exhaust emission limits for diesel engines and diesel vehicles require more and more extraordinary development efforts with respect to reducing both engine-out emissions by improved combustion processes and tailpipe emissions by new exhaust gas aftertreatment systems (EGAS). Today, the main EGAS activities in engine application as well as in research and development concentrates on oxidation catalysts, particulate traps, and DENOX catalysts. This paper deals with 1. a general overview on the development directions of different EGAS and typical emission reduction examples for various diesel engine and vehicle applications : 2. the interaction between legislative emission test cycles, combustion system development and the kind of EGAS used. Based on current development work and test results, ranking considerations with regard to the application and development probability of EGAS are given.?