The law of the flag is a basic principle of maritime and international law. It states that any ship or other vessel is governed by the laws of the nation whose flag is flown by the vessel. This means that anyone who works on or boards the vessel is subject to these laws.
Ships in international waters are the primary places in which the law of the flag applies. As no country's laws apply in these waters, each ship operates under the legal system of the flag it sails under. When a vessel is docked in another country, those aboard the vessel may be subject to local laws, although different countries have their own rules about foreign vessels in their waters.
The existence of the law of the flag is important, as many crews are made up of citizens of different countries. A vessel generally flies the flag of the country in which it is registered. Anyone who boards the vessel agrees to abide by the laws of the vessel's country, regardless of their own nationality or the nationality of the others on board. Theoretically, any breaches of a country's laws on board a vessel that flies that country's flag may ultimately be prosecuted in the courts of that country.
Owners of a vessel may, in some cases, shop around to determine which country's flag to fly. Many political and financial considerations can be involved in choosing the country with which a vessel is to be registered. In these cases, a vessel's owner may take the laws of a country into consideration when choosing which flag to fly.
In some cases, a person may temporarily lease a vessel from its owner. Often, this person will be able to sail under a different flag than that of the country where the vessel is registered. In these circumstances, the vessel flies the flag of the lessee's country.
The law of the flag may also apply to embassies, consulates, or other foreign government offices. A place such as this is a bound area, generally contained within a building or fenced area. It is considered part of the home country, and anyone who enters it is subject to the laws of the country whose flag flies there.