Barter is a system of exchange where goods or services are directly exchanged for other goods or services without using a medium of exchange, such as money. It is distinguishable from gift economies in many ways; one of them is that the reciprocal exchange is immediate and not delayed in time. It is usually bilateral, but may be multilateral (i.e., mediated through barter organizations) and, in most developed countries, usually only exists parallel to monetary systems to a very limited extent. Barter, as a replacement for money as the method of exchange, is used in times of monetary crisis, such as when the currency may be either unstable (e.g., hyperinflation or deflationary spiral) or simply unavailable for conducting commerce.
Economists since Adam Smith, looking at non-specific archaic societies as examples, have used the inefficiency of barter to explain the emergence of money, the economy, and hence the discipline of economics itself. However, ethnographic studies have shown no present or past society has used barter without any other medium of exchange or measurement, nor have anthropologists found evidence that money emerged from barter, instead finding that gift-giving (credit extended on a personal basis with an inter-personal balance maintained over the long term) was the most usual means of exchange of gifts and services.
Since the 1830s, barter in some western market economies has been aided by exchanges that use alternative currencies based on the labour theory of value, and are designed to prevent profit taking by intermediators. Examples include the Owenite socialists, the Cincinnati Time store, and more recently Ithaca HOURS (Time banking) and the LETS system.