2012 Reprint of 1930 Edition. Exact facsimile of the original edition, not reproduced with Optical Recognition Software. This work is an important update and reworking of Fisher's "The Rate of Interest," first published in 1907. Very fundamental changes in the nature of the world economy, principally World War I, war financing, the sensational inflation of the currencies of the combatants, and the remarkable developments in new scientific, industrial and agricultural methods had occurred; all requiring integration into a new theory. Fisher called interest "an index of a community's preference for a dollar of present [income] over a dollar of future income." He labeled his theory of interest the "impatience and opportunity" theory. Interest rates, Fisher postulated, result from the interaction of two forces: the "time preference" people have for capital now, and the investment opportunity principle (that income invested now will yield greater income in the future).