This guideline describes the basis for the choice of methods, the design, operation of facilities and the use of catalysts for catalytic waste gas cleaning. Selective catalytic reduction processes are described. The focus is on the design documentation and examples for the practical use of these methods.The chemism of the catalytic processes and of deactivation of catalysts, catalyst types and the parameters for nitrous oxide reduction rate calculation and for dimensioning of reactors are covered in detail. It contains numerous examples from oil and coal fired power plants, thermal treatment of waste and cleaning of waste gases from motor vehicle combustion as well as marine diesel engines. In addition, special applications are described for reduction of nitrous oxide from nitric acid production.In this guideline operators and planners find emission and operating data of performed plants for which is proven that the selective catalytic reduction is applicable to reduce the exemplified listed pollutants.