Environmental law cannot be treated as international or national; it is both. While environmental concerns have become more and more international in scope during the 20th century, the implementation of international environmental agreements basically remains a matter for national means. This thesis deals with the linkage and compatibility of international and national environmental law. It analyses how and to what extent international environmental law, primarily through various types of treaty obligations, limits the discretion of states in their national implementation. The theory outlined forms the basis for an examination of a large number of international instruments with regard to their adequacy for guiding states towards common environmental objectives. Whilst being confined to pollution control, the ideas and concepts presented are also applicable to other issues of environmental law. Throughout the thesis, the author argues for a relaxation of the distinction between international and national environmental law, e.g. in the decision-making of domestic institutions. Finally, he suggests certain legal elements to be emphasized in the establishment of international regimes on sustainable development.