State jurisdiction over vessels at sea

This book principally examines situations where one state exercises jurisdiction over a vessel otherwise subject to the exclusive jurisdiction of a flag or coastal state. ‘Jurisdiction’ refers to a state's power ‘under international law to govern persons and property by its [national] law’ and to ‘make, apply, and enforce rules of conduct’ to that end. It is commonly held that

State power applied beyond territorial limits seems exceptional, justifiable only by permissive rules or exceptions. The extraterritorial exercise of state jurisdiction over maritime areas and vessels at sea thus requires explanation. International law distinguishes between the scope of prescriptive and enforcement jurisdiction of national criminal law; ordinarily the latter is regarded as absolutely territorially constrained, while the former may extend extraterritorially in certain cases. A state may prohibit or regulate at least certain classes of extraterritorial conduct (‘prescriptive jurisdiction’) even where it has no authority to enforce that law outside its territory (‘enforcement jurisdiction’), such prescription being logically independent of enforcement.