Currency union
two or more states sharing the same currency without them having any further integration
A currency union (also known as monetary union) is an intergovernmental agreement that involves two or more states sharing the same currency. These states may not necessarily have any further integration (such as an economic and monetary union, which would additionally have a customs union and a single market).
There are three types of currency unions:
Informal – unilateral adoption of a foreign currency.
Formal – adoption of foreign currency by virtue of bilateral or multilateral agreement with the monetary authority, sometimes supplemented by issue of local currency in currency peg regime.
Formal with common policy – establishment by multiple countries of a common monetary policy and monetary authority for their common currency.
The theory of the optimal currency area addresses the question of how to determine what geographical regions should share a currency in order to maximize economic efficiency.
Convergence and divergence
Convergence in terms of macroeconomics means that countries have a similar economic behaviour (similar inflation rates and economic growth).
It is easier to form a currency union for countries with more convergence as these countries have the same or at least very similar goals. The European Monetary Union (EMU) is a contemporary model for forming currency unions. Membership in the EMU requires that countries follow a strictly defined set of criteria (the member states are required to have a specific rate of inflation, government deficit, government debt, long-term interest rates and exchange rate).
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