Concept. According to Article 1 of the 1958 Convention on the High Seas, “the high seas mean all parts of the sea that do not fall within the territorial sea or the internal waters of any State. This definition does not correspond to the modern division of maritime spaces according to their legal regime.

There is no definition of the high seas in the UN Convention on the Law of the Sea of 1982. At the same time according to the article 86 the provisions of part VII of the Convention about the high seas are applied to all the parts of the sea which are not included neither in the exclusive economic zone, nor in the territorial sea or internal waters of any state, nor in archipelagic waters of archipelagic state.

This formula can be used to determine the high seas. However, we should note the absence of indication in it of such an important detail: the high seas are not just part of the sea, but its water part, because the bottoms of seas and oceans have a special legal status.
Marine areas beyond which the high seas are located can be united in the territories under national jurisdiction of coastal states: in full (sovereignty) – on internal and archipelagic waters and in territorial sea – on exclusive economic zone in accordance with the norms of international law. There are separate sections in the Convention.

Sometimes the exclusive economic zone is considered as a part of the high seas, “where the right of freedom of the high seas is subject to exceptions in favor of the functional rights of coastal states”.
Such an approach is inconsistent with the need for a clear definition of the legal regime of the various maritime spaces.

The high seas are the watery part of the maritime space beyond national jurisdiction, open for use by all states on the basis of international law.
Legal regime. According to the 1958 United Nations Convention on the High Seas and the 1982 United Nations Convention on the Law of the Sea, the high seas are open to all nations, both coastal and landlocked (inland).

Landlocked states must have access to the sea. To this end, they conclude agreements with landlocked States on transit through their territory, access to seaports and their use.
No State has the right to claim submission of any part of the high seas to its sovereignty.
The regime of freedom of the high seas includes: a) freedom of navigation; b) freedom of flight; c) freedom to lay submarine cables and pipelines; d) freedom to construct artificial islands and other installations; e) freedom of fishing and fishing; f) freedom of scientific research.

Each State shall exercise these freedoms taking into account the requirements of international law and the interests of other States.
Freedom of navigation means that every State, whether coastal or landlocked, has the right to have ships flying its flag on the high seas.

Ships have the nationality of the State whose flag they are entitled to fly. The procedure and conditions of granting nationality to ships, registration of ships and granting the right to fly the flag of one or another state are determined by the domestic legislation, which is formalized by appropriate documents. There must be a real link between the state and the vessel flying its flag. In the practice of international maritime navigation, it is not uncommon to use a “convenient” flag. This refers to cases where the vessel belongs to a company registered in one state and flies the flag of another. Such position can be explained by the fact that some states stipulate simplified or preferential regime of registration, presenting right on flag and vessel exploitation (Liberia, Panama, Malta and etc.).

On the high seas, a ship is subject to the exclusive jurisdiction of the state whose flag it flies. The State exercises its jurisdiction and control in administrative, technical and social matters over ships, the master and crew, maintains a register of ships, takes measures to ensure the safety of navigation, organizes a qualified investigation of every serious accident or other navigation incident on the high seas involving a ship flying its flag. Criminal or disciplinary proceedings against a master or other crew member may only be brought before the judicial or administrative authorities of the flag State.

The Convention provides for a number of exceptions to this principle. A warship may inspect a foreign ship if there are reasonable grounds to suspect that:
1) the ship is engaged in piracy;
2) the ship is engaged in slave trade;
3) the ship is engaged in unauthorized radio and television broadcasting;
4) the ship has no nationality;
5) the ship actually has the same nationality as a warship, although it is flying a foreign flag or refuses to fly a flag.

In addition, an act of intervention is possible if it is based on rules established by international treaties.
For example, International Convention on the Protection of Submarine Telegraph Cables of 1884 gives military ships the right to chase and stop ships suspected of breaking or damaging telegraph cable, check the nationality of the ship, make a report on the breach committed by the ship.

Hot pursuit of a foreign ship is also possible if there are reasonable grounds to believe it has violated the laws and rules of the coastal state in waters under its jurisdiction. The condition for pursuit on the high seas by a warship or military aircraft of a coastal State is its continuity, i.e. it must begin in the maritime areas under the jurisdiction of that State and continue on the high seas. Such pursuit ceases as soon as the pursued vessel enters the territorial sea of its own or another state.
Any acts of interference on the high seas against military vessels and government vessels in non-commercial service are unacceptable.

In order to ensure the safety of navigation and protect other interests of states, international legal norms provide for a number of measures to prevent and suppress certain unlawful acts.

Each State under the 1982 Convention is required to take effective action to prevent the carriage of slaves on ships entitled to fly its flag (Article 39).

Specific measures are envisaged to suppress the crime of piracy. Piracy is defined as any unlawful act of violence, detention or depredation of private ships or aircraft on the high seas, directed against another ship or aircraft, or against persons or property on board.

Any State may seize a pirate ship or aircraft. seize a pirate ship or aircraft on the high seas or elsewhere outside the jurisdiction of any State, arrest the persons and seize the property on board (article 19 of the Convention on the High Seas and article 105 of the Convention on the Law of the Sea). The judicial authorities of the State that has carried out the seizure may order the imposition of penalties and determine the measures to be taken with respect to such vessels, aircraft or property.

All States have an obligation to cooperate in suppressing illicit traffic in narcotic drugs and psychotropic substances carried out by ships on the high seas. If a State has reason to believe that a vessel flying its flag is engaged in illicit traffic in narcotic or psychotropic substances, it may request the cooperation of other States in suppressing such illicit traffic.

States shall also cooperate in suppressing unauthorized broadcasting from the high seas. Unauthorized broadcasting means the transmission of sound radio or television programs from a ship or facility on the high seas intended for reception by the public, in violation of international rules governing telecommunications, the allocation of radio frequencies, etc. Transmission of distress signals cannot be considered unauthorized broadcasting.