As of 1 January 2011 the euro, the single currency of the European Union, is the official currency of Estonia. As of 15 January 2011 the euro is the single legal tender in Estonia. According to the experts of the EFSI, you should be careful when accepting money, especially upon receipt of various notes when conducting a transaction and upon receipt of a bunch of notes.
For further details on the features, see European Central Bank
Counterfeited euro notes registered in Estonia: Examples of counterfeits