The contractors are those private or state-owned companies that carry out exploration and exploitation activities in the Area, which, due to the lack of subjectivity under international law, are not obliged by the UNCLOS. In this book, Xiangxin Xu highlights and analyzes the sponsoring State’s primary responsibility, i.e., ensuring its sponsored contractors’ compliance with environmental obligations under the UNCLOS and related legal instruments by enacting national legislation. She examines how and to what extent the sponsoring State validates and implements the international system at the domestic level and makes up for the shortcomings of the international system in managing contractors. The author further takes China’s legislation as an example and provides how it can be improved.