The phrase international waters suggests an area outside all law. The reality is a layered structure in which coastal authority diminishes with distance and the flag a vessel flies carries jurisdiction everywhere.
Authority is arranged in bands
A coastal state holds sovereignty over a narrow belt of territorial sea measured from its coastline, where its law applies much as it does on land.
Beyond that lies a contiguous zone where a state may enforce customs, immigration and sanitary rules, and then an exclusive economic zone extending considerably further.
Within the economic zone the state controls fishing and seabed resources but not navigation. Foreign vessels may transit freely, which is why the zone is not territory in any ordinary sense.
The high seas belong to no state
Past those zones lie the high seas, open to all states for navigation, overflight, fishing, research and the laying of cables, subject to treaty obligations.
No country may claim sovereignty there. Enforcement therefore depends on states acting over their own vessels and nationals rather than over an area.
Limited exceptions permit any state to act against piracy, unauthorized broadcasting and vessels without nationality, which are treated as offenses against all.
The flag carries the law
Every ship is registered in a state whose law governs it wherever it sails, covering crew conditions, safety standards, taxation and criminal jurisdiction aboard.
Registries differ in what they require, and shipowners choose accordingly. A substantial share of the world fleet flies flags of states with small merchant traditions and open registration.
Enforcement gaps follow from this, since a flag state with limited administrative capacity may inspect rarely. Port states inspect visiting vessels partly to compensate.
Innocent passage has conditions
Foreign ships may pass through territorial seas provided the passage is continuous, expeditious and not prejudicial to the coastal state's peace or security.
Certain acts suspend the protection, including weapons exercises, intelligence gathering, fishing and serious pollution. Submarines must surface and show their flag.
Disputes about whether a particular transit qualifies are among the most common maritime confrontations, and they turn on conduct rather than on the route taken.
Disputes resolve slowly or not at all
The convention establishes tribunals and arbitration procedures, and states have used them to settle boundary questions.
Compliance depends on acceptance, and rulings have been rejected where a state disputes jurisdiction. The framework describes obligations more reliably than it compels behavior.