The flat tax--that is, a single tax rate--may be an idea whose time is coming. The various proposals pending before Congress, however, concentrate on reform and simplification of the personal income tax. Not Hoover Institution economists Hall and Rabushka: their 19 percent flat tax would apply to both individual and business income, and be geared (as they see it) to stimulating the economy. In sum, they advocate a onetime tax on income at the source (eliminating double taxation of dividends); a single tax rate for all taxable income, however derived; an increased personal exemption, so low-income families pay little or no tax; and simple, postcard-sized returns. Answering criticisms that the rich would reap a windfall, they admit that many moderate-income taxpayers would pay more under the flat tax--but say that the improved economy would benefit everyone. To stimulate investment, they would not tax the unearned income of individuals (interest, dividends, capital gains) at all; and business would get an immediate 100 percent write-off of all capital expenditures. In compensation, they suggest an increased personal exemption ($3800 for single taxpayers, $5600 for heads of household, $6200 for married joint filers) and show how this would result in a graduated tax, because the lower a person's income, the more the personal exemption would reduce his or her tax payments and effective tax rate. However, they don't discuss the effect of capital write-off on employment (businesses would have a great incentive to automate jobs out of existence), among many other matters. The book is short, the presentation is lucid, the idea is promising--whether or not the Hall-Rabushka scheme is the way to go.