[Market determination of the value in exchange (price) of money is considered in a general equilibrium finite horizon model. The possibility of the price of money being zero in equilibrium and the role of taxes (payable in money) in preventing a zero price are considered.]

A pairwise trading process is formulated subject to conditions of nonnegativity of traders' holdings and quid pro quo. It is shown that that: (i) There is a centralized procedure that achieves the equilibrium allocation for an arbitrary economy. (ii) It is not in general possible to find a decentralized procedure that achieves the equilibrium allocation for an arbitrary economy. (iii) In a monetary economy there is a decentralized procedure that achieves the equilibrium allocation. The usefulness of money is that it allows decentralization of the trading process.