Innovations in financial markets and in financial management, together with dramatic innovations in the substance and technique of monetary theory, have made it necessary to restate the theory of money and the theory of monetary policy. In order to provide a new monetary theory, the author treats fully the following material: choice of currency and the theory of convertibility; interest on money; speculation and rational expectations; implications of electronic-transfer settlement procedures for monetary theory, as well as other matters. The theories of Tobin are developed and exposited in detail, as is the work of Friedman.