Convertible currency, also known as free foreign exchange, refers to a convertible currency that can be freely converted into other currencies without restrictions. As a convertible currency, the following three conditions must be met: (1) can be freely converted into other currencies; (two) the international current account (that is, trade and non-trade projects) payment is not restricted; (3) The management authorities of currency countries do not adopt or implement multiple exchange rate systems or differential exchange rate systems.

At present, more than 80 countries have declared their currencies as freely convertible currencies. The main convertible currencies are USD, HKD, JPY, SGD, EUR, GBP, CHF, CAD, AUD and NZD.