A single market is not segmented by national regulations, taxes or informal practices.

Non-tariff barriers are different national regulations or practices that prevent free movement of goods, services, and factors across countries.

A monetary union has permanently fixed exchange rates within the union, an integrated financial market and a single central bank setting the single interest rate for the union.

The Maastricht criteria for joining EMU said that a country must already have achieved low inflation and sound fiscal policy.

An optimal currency area is a group of countries better off with a common currency than keeping separate national currencies.

A federal fiscal system has a central government setting taxes and expenditure rules that apply in its constituent states or countries.

Transition economies are making the adjustment from central planning to a market economy.