The designs were agreed upon at the European Council meeting in Amsterdam in June 1997.
The majority of countries only have 3 different back desings - one for each of the groups of coinage, that is one back for the 1,2 and 5 cent, one back for the 10, 20, and 50 cent, and one back for the 1 and 2 euro coins. But some differ from this as well as Finland has one back for all the cent coins and then a 2nd back for the 1 euro and a 3rd for the 2 euro coin. The standard is that there is no standard.
There are 5 countries, Italy, Austria, Finland, Greece, Monaco and San Marino which use multiple back designs. Finland has differing back designs for its 1 and 2 euro coins, the cent coins follow the norm. Italy, Austria, Greece, and San Marino decided to go all out apparently and they have a different back design for each and every coin. Italy, Austria, Greece, and San Marino thus have 8 differnet coin back designs. In the other extreme, Belgium, Ireland, and Vatican City only have 1 back design for all of its coins. The Netherlands has 2 back designs, while Monoco has 4 back designs.
Commemorative coins of various other denominations, not intended for circulation, have been issued. They are legal tender only in the nation which issued them. ...