What Three Seas is and how it works

The criterion, and what it lets in

The initiative describes itself as an economic cooperation platform, established in 2016, of European Union countries geographically located between the Adriatic, the Baltic and the Black Seas. That is two conditions: membership of the Union, and a position between three named bodies of water. The stated purpose is narrower than the geography sounds. It is to develop physical infrastructure and close connectivity gaps in energy, transport and digital infrastructure across the Union's north to south region.

The word doing the work in the criterion is "between". Eight members hold a coast on one of the three seas: Estonia, Latvia, Lithuania and Poland on the Baltic, Croatia and Slovenia on the Adriatic, Bulgaria and Romania on the Black Sea. Austria, Czechia, Hungary and Slovakia have no coast at all. Greece has one on the Ionian, the Aegean and the Mediterranean, and none on the three seas in the name. It was admitted at the summit held in Bucharest in 2023, and that admission is the only movement in the roster since the first meeting.

Dubrovnik, and the statements since

The format was launched in 2015 by Andrzej Duda, president of Poland, and Kolinda Grabar-Kitarović, president of Croatia. Its first summit met at Dubrovnik on 25 and 26 August 2016 and closed with a joint statement on economic cooperation in energy and in transport and communications infrastructure. No treaty was opened for signature, then or since. There is no secretariat, no permanent seat and no budget of its own, and each summit is convened and hosted by one of the members in turn.

Eleven summits had been held by September 2026: Dubrovnik in 2016, Warsaw in 2017, Bucharest in 2018, Ljubljana in 2019, Tallinn in 2020 held online, Sofia in 2021, Riga on 20 and 21 June 2022, Bucharest again in 2023, Vilnius in 2024, Warsaw again in 2025, and Dubrovnik again on 28 and 29 April 2026. Slovakia is to host in 2027. A business forum runs alongside the summit, and the declaration issued at the end is the only instrument the meeting produces.

The gauge, and the direction the rails run

The problem the initiative was set up against is measurable at 85 millimetres. The conventional railway network of Estonia, Latvia and Lithuania is laid at 1,520 millimetres, the gauge of the network it was built into. Rail Baltica is being built at 1,435 millimetres, the standard gauge of the rest of the Union, over 870 kilometres of new electrified line with a maximum design speed of 249 kilometres an hour for passenger trains and 120 kilometres an hour for freight. The European Court of Auditors, reporting in 2020, described it as a missing link in the North Sea Baltic corridor of the trans-European transport network, and put its total estimated cost at 7 billion euro in 2019 values against the 5.8 billion euro then stated officially.

Every member already sits inside the Union's transport, energy and digital rules. The argument the format makes is about the physical connections rather than the rules: that the pipes, cables and track between these countries run east to west across the continent instead of north to south along it, and that planning and money follow the track that exists.

The fund, and who pays into it

The Three Seas Initiative Investment Fund was registered on 29 May 2019 and is the only standing financial instrument the initiative has. It invests in national infrastructure projects in energy, transport and digital communications. The list of contributing states published by Latvia's foreign ministry names Poland, Romania, Estonia, Latvia, Hungary, Bulgaria, Lithuania, Croatia and Slovenia. Austria, Czechia, Greece and Slovakia are not on it, which is the plainest available answer to what a seat costs: a member that puts nothing into the fund keeps its place at the summit. The United States International Development Finance Corporation committed 300 million dollars to the same fund.

Partners, and the chairs beside the table

Strategic partner status is held by the United States, Japan, Germany, Spain, Türkiye and the European Commission, and by Italy from April 2026. Two of those are European Union states with a coast on one of the three seas: Germany on the Baltic, Italy on the Adriatic. Neither takes part as a member, which is where the stated criterion stops accounting for the roster by itself.

A second class sits further out. Ukraine, Moldova, Albania and Montenegro are described as associated partner countries. Ukraine was given the status of a participating partner at the Riga summit of 20 and 21 June 2022. None of the four is in the European Union, so none of them meets the first half of the criterion.

What the records already hold in common

Accession to the Union is the one date every member has, and the dates are spread across more than three decades: Greece on 1 January 1981, Austria on 1 January 1995, Czechia, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia together on 1 May 2004, Bulgaria and Romania on 1 January 2007, and Croatia on 1 July 2013. Austria is the one member with no NATO accession in its record, having stayed outside the alliance since the State Treaty of 15 May 1955 and the neutrality law that followed it in October of that year.

Where the edges are argued

The initiative's account of itself is economic, and readings of it as a political grouping inside the Union are also in print. The catalogue records that both are published and settles neither. What is checkable is what the format does: it convenes heads of state once a year, it issues a declaration, it runs a business forum, and it holds one investment fund. Nothing in it commits a member to a policy, no accession instrument exists to be ratified, and no member has withdrawn.