Before the EIA was established in the Federal Republic of Germany, the impact mitigation principle - a planning instrument, which has its legal foundation in the German nature conservation legislation already had {and still has} the function to valuate environmental impacts. The valuation principles and methods which have been developed in correlation to this instrument are now also used in the EIA. Particularly for the valuation of alternating effects on the different ecological landscape functions and for the valuation of ecological mitigation and compensation measures this valuation methods are used. These methods base on a special kind of modelling nature and environment Following the aim of the nature conservation act, which is to save the capacity of the landscape to perform its essential functions, not the ecological factors (soil, water, air etc.) itselfs are evaluated but the ecological functions of the landscape, which are based on the ecological factors.