The application of countermeasures, traditionally known as reprisal in the field of foreign relations, has been considered a counteract of an injured State in reponse to the prior violation of an obligation within a bilateral context. The World Court in the 1970 Barcelona case confirmed the existence of erga omnes obligaitons for every State with a view to safeguarding the intergrity of the international community as a whole, allowing all States to have a legal interest in protection. The ruling thus may provide some support for the use of unilateral measures to enforce compliance, although the acting State may not suffer tangible damage. However, the legitimacy of specific enforcement remains far from certain. During the past four decades, the International Law Commission (ILC), under the context of State responsibility, has attempted to codify countermeasures in which third-State measures to protect erga omnes interests have also been addressed. A controversy has developed among States as to whether and under what circumstances any State has a right to apply countermeasures in securing the common interests of mankind, such as human rights and the global environment. This article aims to explore the legal status of contemporary third-State countermeasures by examining scholarly arguments and the evolution of international rules mainl referring to the ILC's codification efforts. In particular, it is obvious that nowadays trans-boundary environmental damages and the depletion of global natural resources are serious global problems. A major focus of this article will be the implication of current international developments upon the application of unilateral measures to protect the global environment. Indeed, the final version of the ILC's Articles on State Responsiblity has yet to accord third States entitlement to invoke countermeasures in a strict sense. The Articles nevertheless recognize a unilateral right to apply lawful measures by the incorporation of a saving clause, which may shed some light on third-State enforcement. The arrangement may be an indication of the premature nature of third-State countermeasres. Perhaps, the legality of applying third-party countermeasures cannot by crystallized until a clear and further demonstration of international practices and judicial decision has been made. On the other hand, incontrast to gross violation of human rights, it seems far from clear, apart from huge damage to global commons, under what circumstances injury to international environmental interests may justify the use of third-party remedial actions.