In economics, a medium of exchange is any item that is widely acceptable in exchange for goods and services. In modern economies, the most commonly used medium of exchange is currency.

The origin of "mediums of exchange" in human societies is assumed to have arisen in antiquity as awareness grew of the limitations of barter. The form of the "medium of exchange" follows that of a token, which has been further refined as money. A "medium of exchange" is considered one of the functions of money. The exchange acts as an intermediary instrument as the use can be to acquire any good or service and avoids the limitations of barter; where what one wants has to be matched with what the other has to offer.

Most forms of money are categorised as mediums of exchange, including commodity money, representative money, cryptocurrency, and most commonly fiat money. Representative and fiat money most widely exist in digital form as well as physical tokens, for example coins and notes.