International marine environmental law is not merely a mosaic of specific rules but constitutes a legal system that has coherent relationships between environmental norms on the basis of cardinal principles. An understanding of the systemic aspects of international marine environmental law requires an examination of the basic legal principles and concepts applicable in this field. This chapter examines the basic principles and concepts of international marine environmental law: (1) sic utere tuo ut alienum non laedas (the no harm principle); (2) sustainable development; (3) the precautionary principle/approach; and (4) the principle of cooperation. This chapter first addresses the paradigm shift implicit in international law governing marine environmental protection, before considering the four key principles and concepts, respectively. Finally, the four elements that need further consideration in the development of specific norms concerning marine environmental protection are discussed in conclusion.