The Three Seas Initiative (3SI, TSI)
The Three Seas Initiative, also known as the Three Seas, is a cooperation project aimed at expanding north-south infrastructure connections in the eastern part of the European Union in the areas of transport, energy, and digitalisation.
The idea to establish the Three Seas Initiative was proposed by the Presidents of Poland and Croatia in 2015. The inaugural summit took place in Dubrovnik in 2016. Initially, the 3SI included twelve EU member states, but this number increased to thirteen following Greece’s accession in 2023.
At present, after the Warsaw Summit in April 2025, the Three Seas Initiative includes:
- 13 participating states (only EU members can hold this status): Austria, Bulgaria, Croatia, the Czech Republic, Estonia, Greece, Latvia, Lithuania, Poland, Romania, Slovakia, Slovenia, and Hungary.
- 6 strategic partners – since 2022: the United States, Germany, and the European Commission; since 2024: Japan; and since 2025: Turkey and Spain.
- 4 associated participating states – since 2023: Ukraine and Moldova; since 2025: Albania and Montenegro.
The organisational model of the Three Seas Initiative is based on annual presidential summits (summit diplomacy), during which joint declarations are adopted. The host countries so far have been: Croatia (2016), Poland (2017 and 2025), Romania (2018 and 2023), Slovenia (2019), Estonia (2020), Bulgaria (2021), Latvia (2022), and Lithuania (2024).
Croatia will host the Three Seas Initiative and Business Forum Summit in April 2026.
The 3SI is defined by its participants as “a flexible presidential forum that provides political support to foster more effective cooperation among governments, business entities, and non-governmental organizations interested in strengthening regional ties, while recognizing that achieving tangible results within this initiative requires the active involvement of the respective governments and the maintenance of working-level contacts among the Presidents’ representatives” (from the 2017 Declaration).
The official website of the Three Seas Initiative