Every merchant ship flies a national flag. The flag state is the country under whose laws the ship is registered and whose flag it is entitled to fly; that state has primary jurisdiction over the vessel on the high seas.

Flag states set and enforce safety, labor, and environmental standards, issue certificates, and investigate casualties. Some flags maintain strict oversight; others are criticized as flags of convenience with lighter enforcement. International conventions require flag states to ensure their ships meet minimum standards.

Shipowners choose flags for regulatory environment, tax treatment, and labor rules. Port state control acts as a backstop when flag state oversight is weak. The quality of the flag state directly affects the safety culture and compliance burden aboard the ship.

• Country of a ship’s registration and nationality
• Holds primary jurisdiction on the high seas
• Responsible for safety and environmental standards
• Quality varies widely among registries