Currency substitution is the use of a foreign currency in parallel to or instead of a domestic currency. The process is also known as dollarization or euroization when the foreign currency is the dollar or the euro, respectively.

Currency substitution can be full or partial. Full currency substitution can occur after a major economic crisis, such as in Ecuador, El Salvador, and Zimbabwe. Some small economies, for whom it is impractical to maintain an independent currency, use the currencies of their larger neighbours; for example, Liechtenstein uses the Swiss franc.

Partial currency substitution occurs when residents of a country choose to hold a significant share of their financial assets denominated in a foreign currency. It can also occur as a gradual conversion to full currency substitution; for example, Argentina and Peru were both in the process of converting to the U.S. dollar during the 1990s.