Eurozone participation (Wikipedia). BLUE: 19 EU members in the Eurozone. YELLOW: EU members obliged to join the Eurozone (Bulgaria, Croatia, Czech Republic, Hungary, Poland, Romania and Sweden). PINK: EU member with euro opt-out (Denmark). RED: EU member voting to leave (UK). GREEN: Non-EU mini-states using euro with a monetary agreement (Andorra, Monaco, San Marino, Vatican City). PURPLE: Non-EU states using the euro unilaterally (Kosovo, Montenegro).