Book excerpt: Environmental Impact Assessment (EIA) is a well-established instrument of Environmental Law and policy that aims to ensure that potential adverse environmental effects of human activities are assessed before decisions on such activities are made. The instrument is increasingly being applied in respect of activities that may cause environmental effects across the borders of a state. In this book, thirteen systems of Transboundary Environmental Impact Assessment (TEIA) are assessed that exist or are in development in different parts of the world. Although TEIA is generally associated with EIA between territorial states, this book takes a broader approach and is divided into three sub-parts: Transboundary EIA between states, EIA for activities in international and shared areas, and EIA required by international financial institutions. Knowledgeable experts (scholars and practitioners) provide an overview of the history, content, and practice of the individual systems and, based on these discussions, the state of the art concerning TEIA and possible future developments are discussed.