Eurozone

There is the European Union, which is the free-trade zone and political body encompassing most of Europe. Then there's the eurozone, which is the area made up of all the countries that use the euro as their currency.

You can be part of the European Union and not part of the eurozone. Britain did that for awhile (at least until Brexit). Also Sweden, Denmark, Czech Republic, Croatia, Bulgaria, Romania, Poland, and Hungary.

All told, 19 countries are part of the eurozone (as of 2019). In reverse alphabetical order (just to be different), you've got: Spain, Slovenia, Slovakia, Portugal, the Netherlands, Malta, Luxembourg, Lithuania, Latvia, Italy, Ireland, Greece, Germany, France, Finland, Estonia, Cyprus, Belgium, and Austria.

There are also some countries that use the euro but aren't officially part of the eurozone. Like the neighbor who steals your wifi. Here they are (in order of how close they are to the Pope's house): Vatican City, San Marino, Monaco, and Andorra.