A currency board system is a type of fixed exchange rate regime in which a country's central bank issues a domestic currency that is fully backed by a foreign currency, typically the US dollar or the euro. The central bank commits to maintaining a fixed exchange rate between the domestic currency and the foreign currency by buying and selling its own currency in the foreign exchange market at the fixed rate.

Under a currency board system, the supply of domestic currency is determined solely by the amount of foreign currency held by the central bank. This means that the domestic money supply is fully backed by foreign reserves, and the central bank cannot create new money without acquiring additional foreign currency.

The benefits of a currency board system include low inflation, increased confidence in the domestic currency, and reduced currency risk for investors and businesses. However, the system also has limitations, such as a lack of flexibility in responding to economic shocks and the potential for a sudden depletion of foreign reserves in times of crisis.

Some countries that have adopted a currency board system include Hong Kong, Bulgaria, and Estonia.