How many countries have joined the euro since 1999?

17 countries use the Euro. It came into existence in 1999, coming into circulation in 2002. They are:Austria, Belgium, Cyprus, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Malta, Netherlands, Portugal, Slovakia, Slovenia and Spain.

If you are referring to the European Union, then 13 countries have joined since 1999. Malta, Cyprus, Slovenia, Estonia, Latvia, Lithuania, Poland, the Czech Republic, Slovakia, and Hungary all joined in 2004. Romania and Bulgaria joined in 2007. Croatia joined in 2013.