This thesis investigates the Convention on Access to Information, Public Participation in Decisionmaking and Access to Justice in Environmental Matters (Aarhus). It assesses its normative contribution to International Environmental Politics (IEP). Via English School (ES) lenses, it gauges the degree of pluralism and solidarism in the Convention. More specifically, it evaluates Aarhus’ role as a green human rights regime; scrutinises the contribution of Aarhus’ trinity of procedural rights; offers a regime analysis; and asks (a) what Aarhus’ association with democratisation is and (b) whether its success depends on Parties’ political cultures. Three originality claims are made. First, this project offers a particular investigation into an under-researched, quite elusive Multilateral Environmental Agreement (MEA). Second, it applies pluralism and solidarism to a tangible research object. Third, it addresses the overlooked issue of cosmopolitanisation in IEP. Three key findings are drawn. First, Aarhus demonstrates the presence of, and contributes to, a greener European international society. Second, Aarhus has considerable solidarist potential, offering tools for cosmopolitan human empowerment in IEP. Third, pluralist realities retain distinct influence. Cosmopolitan empowerment may be emerging, but it is still nascent. Sovereignty remains, and this is welcomed. Tentative cosmopolitanisation of political orthodoxies is morally desirable and practically feasible. Evolutionary reform of the statist status quo is more agreeable than revolutionary change. World society values, of the sort enacted by Aarhus, help render IEP more ethically ambitious and human-oriented. But they will not emerge without a stable political framework in which states can institutionalise them. Aarhus demonstrates that whilst IEP remains International, it can still be enriched by humanity, which states must accommodate if they are to be legitimate international citizens, exercising responsible sovereignty, in the twenty-first century.