In this book, Franziska Grashof reconsiders one of the leading principles of European administrative law: the principle of national procedural autonomy. Her work shows that due to different national administrative litigation rules, common European rules are enforced in a fragmented manner. This is illustrated with the example of the judicial enforcement of Directive 2011/92/EU on environmental impact assessment for projects in the legal systems of Germany, England and the Netherlands. Under the same rule of Union law, litigants are treated procedurally unequally, there are different enforcement chances, and judges come to different conclusions not because of diverging interpretations of the law, but because of different administrative litigation rules. Subsequently, it is discussed whether it is necessary, desirable and possible to develop common rules of administrative litigation (in environmental matters) in the Union. It is argued, that by means of the instruments which are available in the Union - specifically legislation, jurisprudence, and comparative scholarship - a more precise common standard for administrative litigation (in environmental matters) should be created, so that the principle is: ubi ius europaeum, ibi remedium europaeum.