Greece voted no in its big referendum, and that looks like the beginning of the end for the euro. Common currencies seemed like a great idea in the 1980s, when currency conversion was a serious source of economic friction. Said the European Commission:

“Before the euro, the need to exchange currencies meant extra costs, risks and a lack of transparency in cross-border transactions. With the single currency, doing business in the euro area is more cost-effective and less risky.”