Money is anything that is generally accepted as payment for goods and services and repayment of debts. The main functions of money are as a medium of exchange, a unit of account, and a store of value. In the past, money was almost always commodity money, money with intrinsic value from the commodity of which it is made (eg. gold and silver coins, shells, tobacco leaves, grain). However, modern monetary systems are based on fiat money – money without intrinsic value, but declared by a government to be legal tender, that is, it must be accepted as a form of payment for 'all debts, public and private'. The term "price system" is sometimes used to refer to methods using commodity valuation or money accounting systems.

The money supply of a country is usually held to consist of currency (banknotes and coins) and 'deposit money' (the balance held in checking accounts and savings accounts). These demand deposits usually account for a much larger part of the money supply than currency. Deposit money is intangible and exists only in the form of various bank records. Despite being intangible, deposit money still performs the basic functions of money, as checks are generally accepted as a form of payment and as a means of transferring ownership of deposit money.