when did poland become part of the eu
2004 enlargement of the European Union At the Luxembourg summit in 1997, the EU accepted the Commission's opinion to invite Poland, Czech Republic, Hungary, Slovenia, Estonia and Cyprus to start talks on their accession to the EU. The negotiation process started on 31 March 1998. Poland finished the accession negotiations in December 2002. Then, the Accession Treaty was signed in Athens on 16 April 2003 (Treaty of Accession 2003). After the ratification of that Treaty in the Polish European Union membership referendum, 2003, Poland and other 9 countries became the members of EU on 1 May 2004.