In Germany, environmental legislation falls to a large extent within the federal government’s legislative powers. But for the implementation of its aims the legislative power of the Laender and local communities is needed as well. Thus a situation can arise where a Federal Law on clean air contains regulations on local power stations, which are at the same time regulated by conflicting local community laws of the Laender. How far is Federal Law in such cases allowed to replace Laender Law? According to the German Constitutional Court, it is the context into which a new rule shall be installed that decides about the legislative competence for it: If it is a Laender law context, it is exclusively up to the Laender to adopt any such rule. However, according to part of the academic opinion, it is the purpose of a rule that decides about the legislative power for it. If it is a purpose belonging to the Federal legislative power the new rule can only be established by Federal legislature. Most convincing appears the approach of the Federal Administrative Court, where it examines the power of federal legislation to interfere with Laender legislation from a plurality of points, particularly the importance of the federal issue and the extent to which Laender legislation is restricted by a federal rule.