Optimal currency areas and customs unions: are they connected?

This paper examines the link between currency areas and customs unions. The size of a bloc of countries practising some form of co-ordination of monetary policy is limited by the incentive to free-ride that formation of the bloc creates. However, when the threat of a trade war is introduced, the stable size of the bloc increases. This suggests that a large currency area is more likely to emerge where it combines with acustoms union, and that the stability of both currency area and customs union are closely related, because the threat of tariff penalties can enforce co-operation.