Most European countries, particularly those in the Mediterranean, accept the Euro as currency. You’ll need Euro for France, Spain, Italy, Portugal, Germany, Greece, The Netherlands, Austria, Belgium, Finland, Slovakia, Lithuania, Slovenia, Estonia, Montenegro, Ireland and Latvia.
In Denmark you’ll need Danish Krone, in Sweden it’s Swedish Krona, in England, Scotland and Northern Ireland it’s British Pounds Sterling, in Iceland it’s Icelandic Krone, in Norway it’s Norwegian Krone and in Russia it’s Russian Rouble.