Slovenia became a member of the European Union on 1 May 2004. The main celebration to commemorate Slovenia’s 20 years in the EU was held on Europe Day, 9 May, in Nova Gorica. The venue is the same as 20 years ago, when the then President of the European Commission, Romano Prodi, welcomed the then Prime Minister of Slovenia, Anton Rop, and Slovenia into the European Union. Nova Gorica will be the European Capital of Culture in 2025, together with Gorizia in Italy, so the central celebration there had an added symbolic significance.

The keynote speakers at the celebration were the current Prime Minister, Robert Golob, and the European Commissioner Janez Lenarčič, who highlighted the advantages of Slovenia's EU membership. The Prime Minister described Europe as a community of values that respects everyone's dignity and gives everyone a chance. He believes that Europe is only strong if it is united, and is only as strong as the bonds of its solidarity. "And the stronger Europe is, the safer Slovenia is", he added.

The focus of the excellent cultural and artistic programme to mark the 20th anniversary celebration was the idea of uniting European nations under one flag and an outline of Slovenia's EU accession history. The performers included the Slovenian music star Vlado Kreslin and world-renowned pianist Alexander Gadjiev. The celebration was complemented by a varied accompanying programme, including a talk by the Minister of Foreign and European Affairs, Tanja Fajon, with selected Slovenia's representatives in the EU institutions, a simulation of the European Parliament and an activity market, a showcase of successful projects supported by EU funds, a discussion between the Minister of Foreign and European Affairs and selected Slovenians working in EU institutions, and a presentation of the European Capital of Culture 2025 programmes. Many related events were held in other parts of Slovenia.