Despite joining the EU in 1994, Sweden still hasn’t joined the euro. Does Sweden have to join the euro? Two countries negotiated an opt-out agreement when they joined the EU – Denmark and the UK – retaining their own currency, but Sweden did not. Why hasn’t Sweden joined yet? In pure technical terms, Sweden has not yet joined the euro because it hasn’t fulfilled one of the necessary criteria – joining the European Exchange Rate Mechanism, also known as ERM II.