Transboundary Environmental impact assessment in International environmental law

Environmental impact assessment is an obligation belongs to International environmental law sphere in order to protect the environment which asks states to determine the likely impacts of a proposed activity or project on the environment of another country or countries. The International Court of Justice has introduced it as a requirement under general international law in pulp mills case and San Juan case pursuant to ITLOS’s explicit recognition of customary status of the EIA. Jurists have different opinions on the EIA, like; the way of becoming a customary rule and especially on the content of it. . Based on the descriptive-analytical methodology with the help of library sources, the present article tried to deduce the process of consolidation, customary status and content of this obligation through international judgments/ awards and documents and concluded that this customary obligation establishes when there is a risk of significant adverse transboundary impact. If there is such a risk, assessment is done. So, there are three stages; the preliminary assessment measuring the possibility of transboundary harm, conducting the assessment and the post-project assessment that provides valuable information for similar subsequent activities and the validity of assessments.