This book analyses a selection of challenges in the implementation and application of the 1982 UN Convention on the Law of the Sea (UNCLOS), focusing on several areas: international organizations, fisheries, security, preserving marine biodiversity, dispute settlement, and interaction with other areas of international law. UNCLOS has been described as the Constitution for the Oceans. It sets out the fundamental rights, obligations and jurisdictions of States regarding the access to, uses and management of the oceans and seas and their resources. It balances States’ diverse and sometimes conflicting interests, such as conflicting uses of space, against navigational interests and the protection of the marine environment. UNCLOS is the first global treaty to include comprehensive obligations on the protection and preservation of the marine environment, including the conservation of living marine resources. These are often common or cross-border challenges, which can only be addressed through international cooperation. The book is divided into three thematic parts. The first concerns the role of international organizations in ocean governance. It includes twelve chapters covering a very diverse set of issues, both materially and geographically, that demonstrate the importance of coordinated actions on the part of multiple States for obtaining harmonized solutions regarding the pursuit of activities in maritime spaces (in connection with e.g. navigation, fisheries or maritime security). The second part concerns the relevance of dispute settlement mechanisms for understanding the international law of the sea and the international legal framework within which the actions of the great maritime powers take place. It is composed of three chapters, examining stakeholders’ role in dispute settlement, the position taken by China and the Russian Federation regarding international litigation in maritime spaces, and how the South China Sea Award may be relevant to the debate on the international legal concepts of rock and island. In turn, the third part addresses current discussions on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction. Its seven chapters report on the status quo of the ongoing negotiations for a new international legal regime of the high seas, and the establishment and operationalization of environmental regimes for international maritime spaces.