The value of the Estonian Kroon (eek) was fixed to the ?. The smaller unit was called the Cent, 1 kroon = 100 cents. 1 EUR = 15,65 kroons(EEK).
On the 1st of January 2011, Estonia joined the euro-zone and switched the Estonian Kroons to euros.
During the adoption phase, shops (and other establishments) displayed the prices both in kroons as well as euros and it still may be the case in some shops.
Seeing two currencies on a price tag may feel just a tiny bit confusing, but the only official currency in Estonia is euro and hopefully, all of the price tags will be updated soon.
Changing money in Estonia is easy at the many ATMs, banks, hotels and bureaux de change that offer currency exchange services.
Credit cards such as Visa and Mastercard/Eurocard etc. are accepted in most of the major hotels, restaurants and shops. Use of American Express is not as common.