Coincidence of wants

The coincidence of wants problem (often "double coincidence of wants") is the situation where the supplier of good A wants good B and the supplier of good B wants good A

It is an important category of transaction costs that impose severe limitations on economies lacking a medium of exchange (such as money), which have to rely on barter or other in-kind transactions. The problem is caused by the improbability of the wants, needs, or events that cause or motivate a transaction occurring at the same time and the same place. One example is the bar musician who is "paid" with liquor or food, items which his landlord will not accept as rent payment, when the musician would rather have a month's shelter. If, instead, the musician's landlord were to throw a party and desire music for it, hiring the musician to play it by offering the month's rent in exchange, a coincidence of wants would exist.