Part I has highlighted that the authors advocating an environmental non-regression principle are certainly right to look into international human rights law for inspiration, as such a principle can indeed be discerned from universal and regional human rights regimes. By contrast, it was found in Part II that whilst some of the substantive provisions of environmental agreements appear to come very close to the idea of progressive implementation and non-regression, such concepts have not (yet) been systematically developed by most MEA treaty bodies. The Paris Agreement is one of the few examples where closely similar concepts have expressly found entrance into the treaty text. Against this background, one may return to the scholarly suggestions noted in the Introduction, which have called for the recognition of non-regression as a principle of IEL. In the following, it will be discussed whether non-regression can be considered an already established free-standing principle of IEL (Chapter 7). In addition, an alternative suggestion will be pursued that focuses on the potential for mutual inspiration between human rights law and IEL. An appropriate framework for structured and systematic receptions from one subject-specific area of international law (human rights law) into another area (IEL) can arguably be developed by revisiting the utility of comparative law methods in international law (Chapter 8).