The article addresses the normative hierarchy in international law of the principle according to which States have the responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of ther States or of areas beyond the limits of national jurisdiction. The analysis focuses on three concepts which entail certain hierarchy in international law, namely those of peremptory norms, obligations erga omnes and essential interests. The author concludes that, in the present state of international law, the principle of environmental protection constitutes both an obligation erga omnes and an essential interest of the State, capable of founding an allegation of state of necessity. At the same time, this principle has a significant heuristic value to the extent that it provides an illustration of the differences between the concepts of obligations erga omnes, esencial interests and that of peremptory norms.