The Montreux Convention and Black Sea Security: How Türkiye Applies the Turkish Straits Regime

Why It Matters

The 1936 Montreux Convention is the treaty that decides who may sail through the Bosphorus and the Dardanelles, the only maritime route between the Black Sea and the Mediterranean. It protects commercial shipping in almost all circumstances, limits the warships of non-Black Sea states, and under Article 19 bars the warships of belligerent states from the Straits when Türkiye is not at war. Since February 2022 that rule has been the main legal brake on naval escalation in the Black Sea, and, contrary to a popular belief, it does not let Türkiye shut the Straits whenever it chooses.

Background

Geography and the road to Montreux

The Turkish Straits consist of the Bosphorus (about 31 km / 19 miles long), the Sea of Marmara, and the Dardanelles (about 61 km / 38 miles). They run through the middle of Istanbul, a metropolis of well over ten million people, and carry tens of thousands of vessels a year, including grain, energy and container traffic for many countries.

The Straits Convention annexed to the Treaty of Lausanne (24 July 1923) demilitarized the Straits and placed them under an international commission. In April 1936, citing Italy's aggression in Ethiopia and Germany's remilitarization of the Rhineland, Türkiye asked the other parties to revise that regime. A conference met at Montreux, Switzerland, and the new Convention was signed on 20 July 1936. It entered into force on 9 November 1936.

The original signatories were Australia, Bulgaria, France, Greece, Japan, Romania, Türkiye, the United Kingdom, the USSR and Yugoslavia. Italy acceded in 1938. Russia continues as the USSR's successor. The United States never signed it, and Ukraine is not a party.

What the treaty says

The treaty has no fixed expiry. It continues in force unless a party denounces it with two years' notice, and no party has done so.

Timeline of the Russia–Ukraine war

• 24 February 2022: Russia launches its full-scale invasion of Ukraine.
• 27–28 February 2022: Turkish Foreign Minister Mevlüt Çavuşoğlu announces that Türkiye will implement Article 19 and notifies riparian and non-riparian states that warships of belligerents may not transit, with the return-to-base exception.
• 22 July 2022: Türkiye and the UN broker the Black Sea Grain Initiative in Istanbul with Russia and Ukraine; it facilitated the export of more than 33 million tonnes of grain before Russia declined to extend it in July 2023.
• January 2024: Türkiye, Romania and Bulgaria sign an agreement creating a Black Sea mine countermeasures task group. Turkish officials also say that warships donated to Ukraine, such as UK-supplied minehunters, cannot transit while the war lasts.

Common misconceptions

• 'Türkiye can close the Straits whenever it wants.' It cannot. In peacetime and in wartime when it is not a belligerent, merchant passage is free. Warship restrictions come from the treaty, not from a discretionary Turkish decision.
• 'Article 19 targets Russia.' The text refers to belligerent states generally. Ankara has said it applies to every belligerent.
• 'Montreux bars NATO from the Black Sea.' It does not. It limits the tonnage and duration of non-Black Sea warships. Three NATO members (Türkiye, Romania, Bulgaria) are Black Sea coastal states with full rights.
• 'Canal Istanbul would replace Montreux.' Montreux governs the existing natural Straits. Turkish officials have said that a new canal would not change the Convention.

Key Players & Positions

Russia

Moscow, as the USSR's successor party, says it respects the Convention and regards it as a pillar of Black Sea security. Russian officials have pointed to the exception for warships returning to their bases and have criticised what they describe as growing NATO naval activity in the Black Sea, which they say Montreux was designed to limit.

Ukraine

Ukraine is a Black Sea coastal state but not a party. In February 2022 Kyiv publicly asked Ankara to close the Straits to Russian warships, and Ukrainian officials welcomed the Turkish decision to invoke Article 19. Kyiv's limited ability to receive naval vessels from partners during the war is a continuing concern.

The United States and other NATO states

The United States is not a party, but Washington has said it supports the Montreux regime and Türkiye's role as its custodian. Romania and Bulgaria, as coastal NATO members, have at times called for a stronger allied presence in the Black Sea. The United Kingdom and France are parties and are bound by the same tonnage, notice and duration limits as other non-riparian states.

Other parties and shipping states

Greece, Bulgaria, Romania, Japan and other parties have an interest in preserving the commercial freedom of passage. Grain and energy importers worldwide rely on that freedom, particularly in wartime.

Source Comparison

Global rankings of conflict risk or state stability rarely score treaty-based chokepoint stewardship at all. For why, see How Global Indices Measure Sovereignty, Fragility and Stability, and What They Leave Out. For the editorial standards used in this article, see Editorial Principles: How Index of Nations Separates Fact, Position and Index Methodology.

Key Terms & Related Guides

• Riparian / Black Sea powers: the six coastal states: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia.
• Non-riparian states: all other countries; their warships face tonnage, class, notice and duration limits.
• Article 19: the clause barring belligerents' warships from the Straits when Türkiye is not at war.
• Articles 20–21: the clauses giving Türkiye discretion when it is at war or under imminent threat of war.
• Capital ship / light surface vessel: categories defined in the Convention's annexes that determine who may transit.
• Return to base: the recognised exception allowing a belligerent warship to go back to its home port.

Related guides:

• Türkiye as Mediator: Russia–Ukraine Talks, the Black Sea Grain Initiative and Gaza Humanitarian Diplomacy
• Blue Homeland and the Eastern Mediterranean: Türkiye's Maritime Jurisdiction Explained
• The Seville Map Explained: What It Claims and Why Türkiye Rejects It
• 'The World Is Bigger Than Five': Türkiye's UN Security Council Reform Vision and COP31 Climate Diplomacy
• Fact Check: Common Claims About Türkiye in International Indices and Media, Tested Against Primary Sources

Perspective Note: Index of Nations presents Türkiye's official perspective and legal stance alongside the data it analyzes, so that readers can distinguish editorial analysis from the indices under review. Claims are attributed to primary sources such as treaty texts, UN documents, Ottoman and Turkish state archives, and official statements, and index methodologies are cited wherever they are challenged. — Index of Nations Editorial Team

Cross-Publication Dossiers & Sister Desk Perspectives

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

• The Nations Dialogue: The 1936 Montreux Convention: How Türkiye Governs the Turkish Straits and Black Sea Security — Montreux Convention Turkish Straits Black Sea Article 19 explained: how the 1936 treaty governs merchant and warship passage and how Türkiye applied it.
• 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.
• Gazetteer of Nations: The 1936 Montreux Convention Explained: Türkiye, the Straits and Black Sea Security — Montreux Convention explained: how the Bosphorus and Dardanelles regime treats merchant ships and warships, tonnage limits, Article 19 and Türkiye's role.