The Lublin Triangle (Lithuanian: Liublino trikampis; Polish: Trójkąt Lubelski; Ukrainian: Люблінський трикутник, romanized: Liublinskyi trykutnyk) is a regional alliance of three European countries – Lithuania, Poland, and Ukraine – for the purposes of strengthening mutual military, cultural, economic and political cooperation and supporting Ukraine's integration into the European Union and NATO. The Lublin Triangle initiative invokes the integrative heritage of the 1569 Union of Lublin.

The Lublin Triangle countries declare their support for restoring Ukraine's territorial integrity within internationally recognized borders and call for an end to Russian aggression against Ukraine. The Lublin Triangle supports granting Ukraine the status of NATO enhanced partner and considers a NATO Membership Action Plan for Ukraine to be the next necessary step in that direction.

The tripartite format draws on the traditions and historic ties of the three countries. The pertinent joint declaration was adopted by the several ministers on 28 July 2020 in Lublin, Poland. Lublin was chosen in deliberate reference to the 1569 Union of Lublin that created the Polish–Lithuanian Commonwealth, then one of the largest countries in Europe.

A joint declaration by the Foreign Ministers of Lithuania, Poland and Ukraine, Linas Linkevičius, Jacek Czaputowicz and Dmytro Kuleba, on the creation of the format was signed on 28 July 2020 in Lublin, Poland.

On 1 August 2020 the Minister for Foreign Affairs of Ukraine Dmytro Kuleba invited the Minister of Foreign Affairs of Belarus Vladimir Makei to the second meeting, which is to take place in Kyiv. During the Economic Forum in Karpacz, Poland, on 10 September 2020, Jan Hofmokl, Director of the Eastern Department of the Polish Foreign Ministry, stated that the Lublin Triangle should in fact be a square with Belarus. According to him, at the initial stage Minsk was interested in this political project, but later changed its mind.

On 17 September 2020 the first meeting (in the format of a video conference) of the national coordinators of the Lublin Triangle, created by the Foreign Ministers of Ukraine, Poland and Lithuania in July 2020, took place. Vasyl Bodnar (Ukraine), Marcin Przydacz (Poland) and Dalius Čekuolis (Lithuania), Deputy Foreign Ministers, have been appointed coordinators of this tripartite cooperation mechanism. The parties discussed preparations for the next meeting of the Foreign Ministers of the Lublin Triangle, which is to take place in Kyiv on the initiative of Minister Dmytro Kuleba. One of the main tasks of the Lublin Triangle should be to coordinate the actions of Ukraine, Poland and Lithuania to effectively counter the challenges and threats to common security, among which the priority is to counter hybrid threats from Russia.

On 29 January 2021, during the first online meeting of the Lublin Triangle, Ukrainian Foreign Minister Dmytro Kuleba stated at a briefing that Ukraine, Lithuania and Poland are in favor of Belarus joining the Lublin Triangle, but the time has not yet come.

"Of course, without Belarus, the Lublin Triangle is a bit incomplete. We would like, in the end, democratic Belarus to join and turn the "Lublin Triangle" into the Lublin "square". But the time for this has not yet come. At the same time, we all understand that the situation in Belarus has an impact not only on the country's bilateral relations with its neighbors, but also on the situation in the region as a whole." - Kuleba said, summing up the first meeting of the Lublin Triangle.