 The concept of “exchange” is at the core of the concept of markets. In markets, exchanges of goods and services take place for reasons of self-interest, in contrast to, for example, the exchange of gifts with the aim of building relationships (on gift exchange see e.g., Maus 1923–24). Most markets use money as a medium of exchange. Often, individuals act as “price takers”, i.e., they take prices as given and choose how much to buy or sell. But there are also markets where exchanges take place in the form of barter or in different forms of auctions. The concept of “markets”, however, is wider than the concept of exchange because it includes the structural macro-effects that result from a large number of exchanges, for example changes in the overall price level.