This book critically analyses the availability of environmental counterclaims in investment arbitration presented by the respondent host state against the claimant investor. It starts from the premise that the conflicting relation between investment law and environmental protection cannot always be avoided. Yet, the instrument of environmental counterclaims in investment arbitration might alleviate such relation. Throughout its chapters, this book addresses the questions about the societal and practical relevance of seeking redress for environmental damage in investment arbitration, the functioning of such instrument both in contract-based and treaty-based investment arbitration, the suitability of arbitral tribunals to rule upon environmental issues, and the kind of environmental damages that could be redressed. Most importantly, by deconstructing the requirements of jurisdiction, connection between main claim and counterclaim, and cause of action, this book provides the tools for there-conceptualisation of the instrument of counterclaims with the hope of harnessing its utility to achieve appropriate redress for environmental damages caused by foreign investors.