This book explores the scope and applicability of The United Nations Conventions on Law of the Sea ('UNCLOS'), chapter XII, relating to the enforcement of international environmental maritime legislation. In so doing, it clarifies the increased enforcement and information obligations placed on flag States and the broadened jurisdictional basis for port and coastal States. Its examination extends the enforcement provisions in The International Convention for the Prevention of Pollution from Ships ('Marpol'), Annex VI, including by port States on the high seas. The book also applies the same principles of enforcement through chapter XII of UNCLOS on both existing and future environmental regulation. Finally, given increased environmental challenges, the book offers an analysis of whether certain international environmental legislation in the future could be considered peremptory norms protected by the jus cogens principle to counter global warming, climate change and overall air pollution.