Since ancient times, governments have produced coins to establish a predictable form or currency for their citizens. Thus, Canada and the United States have their dollars, Russia has its ruble, people in China exchange yuans for goods and services, and countries from England to Australia execute trades of all sorts in pounds.
Until not too long ago, the European continent was a happy hodgepodge of different denominations. Parisian croissants were paid for in francs, a glass of good German beer would cost you a few marks, and a Spanish paella could only be had in pesetas. Today the euro reigns over Europe, except in Great Britain, where pounds still exchange hands, and Denmark, which has yet to let go of its beloved krone.