Recent years have seen an explosive increase in investor-state disputes resolved in international arbitration. This is significant not only in terms of the number of disputes that have arisen and the number of states that have been involved, but also in terms of the novel types of dispute that have emerged. Traditionally, investor-state disputes resulted from straightforward incidences of nationalisation or breach of contract. In contrast, modern disputes frequently revolve around government measures taken to further public policy goals, such as the protection of the environment. This book explores the outcomes of several investor-state disputes over environmental policy. In addition to examining the pleadings of parties and decisions of arbitral tribunals in disputes that have been resolved in arbitration, the influence that investment arbitration has had in negotiated outcomes to conflicts is also explored.