The Maastricht Treaty, which was signed in February 1992 and entered into force on 1 November 1993, outlined the five convergence criteria EU member states are required to comply with to adopt the new currency, the euro.
The first full convergence report was published in November 1996, and concluded only 3 out of 15 EU member states (Denmark, Luxembourg and Ireland) were completely compliant with the criteria at that point in time.
[17] In March 1998 a more positive second convergence report concluded that 11 out of 12 applying countries were prepared for the electronic introduction of the euro on 1 January 1999, with only Greece failing to qualify by the deadline.
[18] Subsequent convergence reports have so far resulted in an additional 9 EU member states complying with all criteria and adopting the euro (Greece, Slovenia, Cyprus, Malta, Slovakia, Estonia, Latvia, Lithuania and Croatia).
The latest convergence report was published in June 2014, and checked for compliance in the reference year from May 2012 – April 2014, where Lithuania managed to fully comply – thus becoming the next 19th eurozone member.
[6] As the reference values for HICP inflation and long-term interest rates change on a monthly basis, any member state with a euro derogation has the right to ask the ECB for an updated compliance check, whenever they believe they have met all both economic and legal convergence criteria.
As reference values for HICP and interest rates are subject for monthly changes, any EU member state with a euro derogation, has the right to ask for a renewed compliance check at any time during the year.
[6][13] As of 12 September 2014, all of the remaining euro derogation states without an opt-out had not yet entered ERM-II,[20] which mean it's highly unlikely any of them will ask the European Commission to conduct an extraordinary compliance check ahead of the publication of the next regular convergence report (scheduled for release in May/June 2016).