“Climate Protection Law” has been developed during the last approximately 15 years on an international, supranational and regional level. In the European Union the trading scheme of greenhouse gas allowances—introduced by Directive 2003/87—is to be considered a central element of the European Union’s climate protection policy. Despite of the creation of the EU emission trading scheme already in 2003 the scheme raises a range of legal questions which have not been really clarified yet. Against this background, the following contribution will discuss—on the basis of a summary of the legal bases and the development of emission trading in the EU—some selected legal questions concerning design, interpretation and application of the Directive 2003/87. Additionally, the question of whether the emission trading scheme as provided by Directive 2003/87 could serve as a model for air protection respectively emission reduction of other air pollutants and / or as a model for a trans-regional or even global emission trading scheme will be discussed.