Should deep seabed mining (DSM) stop or proceed? The international community is now facing a difficult choice. No matter what decision is made, environmental consideration is the core of the issue. This book tackles the compelling question of how to secure the marine environmental protection in DSM from an international law perspective. It deals with two major research questions: What are the international environmental requirements of participants the contractor, the sponsoring State and the International Seabed Authority (ISA)? What are the legal consequences for them when environmental damage occurs? In doing so, it analyses the international DSM legal regime and general international environmental principles, observes the functioning of the ISA, and draws on law and practice of various environmental treaty mechanisms. The examination reveals the potential practical difficulties as well as fundamental obstacles in the application of international environmental rules and principles in the specific context of DSM.