This article argues that the International Court of Justice's (ICJ) account of the customary law of environmental impact assessment (EIA) is incomplete. While acknowledging the role of the harm prevention principle in formulating the customary obligation to conduct EIAs, the ICJ has ignored the duty to cooperate, notwithstanding the latter duty's equally strong standing in international environmental law. Ignoring the duty to cooperate pushes the court towards a formal and sequential understanding of EIA, which undervalues the centrality of notice and consultation in EIA. In effect, viewed through the harm prevention lens alone, EIA is largely understood in instrumental and technical terms; whereas, if the duty to cooperate is brought back in, EIA's deliberative and ‘other-regarding’ nature is more clearly seen. This, in turn, recognises the normative and political role of EIA in structuring State interactions respecting environmental disputes.
