As of my knowledge cutoff in September 2021, 19 out of the 27 member states of the European Union use the Euro as their official currency. These countries are Austria, Belgium, Cyprus, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Portugal, Slovakia, Slovenia, and Spain. The remaining eight EU member states, namely Bulgaria, Croatia, Czech Republic, Denmark, Hungary, Poland, Romania, and Sweden, have not adopted the Euro yet. Each country has its own timeline and criteria for joining the Eurozone, and some have opted to maintain their national currencies for various reasons, such as economic considerations or popular sentiment.