In the nearly five decades since the publication of Irving Fisher’s The Theory of Interest, economists have engaged in numerous attempts to measure the ex-ante real rate of interest. The effort devoted to obtaining these estimates reflects the fact that the ex-ante real interest rate conveys information about some fundamental economic relationships. The ex-ante real interest rate is the expected net rate of increase in wealth arising from additional investment. Alternatively, it can be viewed as the value of present consumption in terms of future income and, consequently, is implicit in the relative price of present consumption in terms of capital goods. Each of these is reconciled with the others by the profit-seeking market activity of individuals.