What Is the Montreux Convention and How Does It Govern the Turkish Straits?

By the WPD Editorial Team

Why It Matters

The 1936 Montreux Convention is the treaty that decides which ships can sail between the Black Sea and the Mediterranean. It gives Türkiye, which controls the Bosphorus and the Dardanelles, defined powers over warship traffic while keeping commercial shipping free. Since Russia's full-scale invasion of Ukraine in February 2022, this old treaty has become central to Black Sea security. For a wider regional picture, see Black Sea Security and the Turkish Straits: A Complete Guide.

Background: How the Regime Came About

The Montreux Convention replaced the Straits regime of the 1923 Treaty of Lausanne. That earlier regime demilitarised the Straits and put them under an international commission. By the mid-1930s, Türkiye argued that this arrangement no longer matched the security situation in Europe. It asked the Lausanne signatories to renegotiate.

A conference met in Montreux, Switzerland, and the Convention Regarding the Regime of the Straits was signed on 20 July 1936. It entered into force on 9 November 1936. The original parties included Türkiye, the United Kingdom, France, the Soviet Union, Bulgaria, Greece, Romania, Yugoslavia, Japan and Australia. Italy joined in 1938. Today the Soviet Union's seat is held by Russia, and several other original parties have changed form or no longer take an active part.

The Convention covers three connected waterways: the Dardanelles, the Sea of Marmara and the Bosphorus. Together they form the "Turkish Straits." The Bosphorus runs through Istanbul, a city of many millions, and is roughly 30 km (19 miles) long. The Dardanelles is roughly twice that length.

Two features define the treaty:

• It lets Türkiye remilitarise the Straits zone, which Lausanne had forbidden.
• It transfers the supervisory role of the old international commission to the Turkish government. Türkiye collects information on traffic and reports on it to the parties.

What the Montreux Convention Says

The Convention sets out a general principle of free passage and then adds detailed rules by ship type and by whether the situation is peace or war. Article 1 affirms "the principle of freedom of transit and navigation by sea" in the Straits. Article 28 provides that this principle continues without limit of time.

Merchant ships

Merchant ships get the most open regime. In peacetime they have freedom of passage by day and night, whatever their flag or cargo. They are subject to health (sanitary) inspection, and Türkiye may charge fees for specific services listed in the Convention's annex, such as lighthouses or pilotage. Pilotage and towage are optional.

In wartime the rules depend on Türkiye's status:

• Türkiye not at war: merchant ships keep freedom of passage, including ships of belligerent states.
• Türkiye at war: merchant ships not belonging to a country at war with Türkiye keep the right of passage, as long as they do not assist the enemy. Turkish authorities may direct them to specific routes.

Warships: the Black Sea / non-Black Sea divide

The Convention treats warships very differently depending on whether their flag state has a Black Sea coast. Black Sea states are Türkiye, Russia, Ukraine, Romania, Bulgaria and Georgia. Everyone else is a "non-Black Sea state."

Rule	Black Sea states	Non-Black Sea states
Notice before transit	8 days (diplomatic channels)	15 days
Eligible ship types	Light surface ships, minor war vessels, auxiliary vessels; capital ships above 15,000 tons may pass singly, escorted by no more than two destroyers	Light surface ships, minor war vessels, auxiliary vessels only
Maximum size of an individual ship	Larger capital ships allowed under the escort rule	Generally 15,000 tons
Submarines	May transit, if built or bought outside the Black Sea, with prior notice; also for repair or return to base	Not permitted
Ships in transit at once	Not capped in the same way	No more than nine
Presence in the Black Sea	Unrestricted by tonnage	Aggregate cap of 30,000 tons, rising up to 45,000 tons if the strongest Black Sea fleet grows; one state limited to two-thirds of the aggregate; stay limited to 21 days

Aircraft carriers are not among the types allowed through. The Soviet Union's Kiev-class ships, classed as "aircraft-carrying cruisers," were a historic point of debate over where the line falls.

Peacetime versus wartime for warships

In peacetime, the table above applies. In wartime there are three situations:

1. Türkiye is not a belligerent (Article 19). Warships of belligerent states may not pass the Straits. The exceptions are certain obligations under collective security treaties set out in the Convention and the return of ships to their home bases.
2. Türkiye is a belligerent (Article 20). The passage of warships is left to the Turkish government's discretion.
3. Türkiye feels threatened by imminent danger of war (Article 21). It may likewise exercise that discretion.

In practice, Türkiye decides when these provisions apply. That is the source of both the treaty's flexibility and the debates over its use.

Key Players and Positions

Türkiye is the guardian of the Straits and the party that applies the Convention. See the "Türkiye's Position" section below.

Russia is a Black Sea state with its Black Sea Fleet based in Crimea and Novorossiysk. It values the Convention because it limits the time and size of NATO naval presence in the Black Sea. Russian officials have said the Convention must be respected, and they have also pointed to the home-base exception for Russian ships.

Ukraine has urged Türkiye to block Russian warships. Kyiv welcomed the 2022 decision.

NATO members with a Black Sea coast (Türkiye, Romania, Bulgaria) and other allies operate within the tonnage and duration limits. The United States, as a non-Black Sea state, is subject to them when it sends ships into the sea. The US is not a party to the Convention but has historically operated within it.

Other Black Sea states (Georgia, Bulgaria, Romania) generally support keeping the treaty as it is. The balance the Convention strikes is widely seen as a stabilising factor.

Application After February 2022

Russia launched its full-scale invasion of Ukraine on 24 February 2022. Ukraine asked Türkiye to close the Straits to Russian warships. Türkiye's Foreign Minister said on 28 February 2022 that Ankara considered the situation a war and would implement Article 19, warning both Black Sea and non-Black Sea states not to send warships through. Turkish officials said this applied to all belligerents, not only Russia.

What this meant in practice:

• Return-to-base ships could still transit. Turkish officials said they were applying that exception strictly and had turned down some requests, including some from Russia, and some from non-Black Sea states.
• Non-belligerent warships of NATO members remain subject to the usual notification and tonnage rules.
• Merchant traffic was not closed. Commercial passage continued, which made the 2022 Black Sea Grain Initiative possible. For how that deal worked, see How Did the Black Sea Grain Initiative Work and What Was Türkiye's Role?.
• In January 2024, Türkiye, Romania and Bulgaria signed an agreement on cooperation against naval mines in the western Black Sea.

Critics have raised questions on both sides. Some in Ukraine and in the West wanted a broader closure, including of the return-to-base exception. Some in Russia argue that the interpretation constrains Russia's ability to move ships between fleets. Turkish officials respond that the Convention's text, not preference, defines what they can do.

🇹🇷 Official Policy · Primary Turkish Sources

Türkiye's Position

This section reflects official Turkish policy as stated by Turkish government sources. It is separate from the analysis above.

• The Convention is a balance, and Ankara wants to keep it. According to the Turkish Foreign Ministry, Montreux balances Türkiye's security, freedom of commercial passage and the security of Black Sea states. Ankara has said it sees no need to reopen the text. Legal basis: Articles 1 and 28 of the Convention.
• Article 19 applies equally to all belligerents. In its February 2022 statements, the Foreign Ministry and the Turkish Foreign Minister said Türkiye would apply Article 19 to every party to the war, without discrimination. Ankara argues that this is the only approach consistent with its neutral role in the conflict and with the treaty. Legal basis: Article 19.
• Türkiye maintains the return-to-base exception. Ankara says the treaty itself provides for ships returning to home base, and that it will apply that exception on the basis of documentation, not politics. Legal basis: the final part of Article 19.
• Türkiye's discretion is part of the text. The Turkish government states that the Convention gives it the responsibility to judge when a war exists. It also points to Articles 20 and 21 as protecting Türkiye's own security. Legal basis: Articles 19 to 21.
• Diplomacy runs alongside the treaty. Türkiye says it can only mediate and host talks, as it did in the grain deal, because it applies the Convention impartially.

Readers can compare these points against the Convention text, which is published by the Turkish Ministry of Foreign Affairs and in the League of Nations Treaty Series, and against the Ministry's statements and the Presidency's communications office releases. For how we distinguish fact from position, see our Editorial Principles.

Source Comparison

Different outlets frame the same facts differently.

• Turkish official sources stress legality, neutrality and the treaty's long record of stability. The emphasis is on process: Article 19 was invoked, and Ankara says it applies equally to all.
• Western media often describe Türkiye as a "gatekeeper" and focus on its leverage and balancing between NATO and Russia. Some coverage frames the decision as a favour to Ukraine, while others stress how little practical effect closure had on Russia's fleet already inside the Black Sea.
• Russian official sources tend to stress treaty compliance, the home-base exception, and concern about NATO's presence near Russian shores.
• Ukrainian sources emphasise the legal basis for blocking Russian warships and call for stricter enforcement.

Where claims about Türkiye's role are disputed or misreported, we address them in our Fact Check: Claims About Türkiye in International Media series.

Glossary

• Turkish Straits: the Bosphorus, Sea of Marmara and Dardanelles.
• Black Sea state (riparian): a country with a Black Sea coast. Under the Convention these have more privileges than others.
• Non-Black Sea state: any other country; its warships face tonnage and duration limits.
• Capital ship: a large warship, defined in the Convention by size and armament.
• Article 19: the clause barring belligerent warships from the Straits when Türkiye is not at war.
• Home-base exception: the provision letting belligerent ships return to their bases.
• Aggregate tonnage: the total weight of foreign naval forces allowed in the Black Sea at once.

For background on the wider system, see WorldPoliticsDaily: World Politics Explained in Plain English and About WorldPoliticsDaily.

Perspective Note

WorldPoliticsDaily presents global affairs with a dedicated perspective from Türkiye. Sections marked "Türkiye's Position" reflect official Turkish policy as stated by Turkish government sources.

Cross-Publication Dossiers & Sister Desk Perspectives

For complementary primary-source analysis across our specialist editorial network, consult:

• Region Scope: The Montreux Convention Explained: How Türkiye Manages the Turkish Straits and Black Sea Security — What is the Montreux Convention and the Turkish Straits regime? Learn the 1936 rules on warships, Article 19, Black Sea balance and Türkiye's role.
• Index of Nations: The Montreux Convention and Black Sea Security: How Türkiye Applies the Turkish Straits Regime — Montreux Convention Turkish Straits explained: merchant freedom, warship limits, Article 19 in the Ukraine war, and why Türkiye can't close them at will.
• Horizon of Nations: The 1936 Montreux Convention: How Türkiye Manages the Turkish Straits in the Black Sea War — How the Montreux Convention governs the Turkish Straits: commercial passage, warship limits, Article 19 in the Black Sea war, and the views of all sides.