The classical Capital Asset Pricing Model of Sharpe [5] and Lintner [4] has been generalized by Brennan [2, 3] to include the effect of investors' taxes. In Brennan's formulation, investors' portfolio incomes are divided into capital gains and ordinary income components whose marginal tax rates differ both from one another and across investors. In this paper, Brennan's model is further generalized to admit tax–exempt portfolio income as well. The results, which may accord with empirical data better than have those of the less general models, include a three–fund separation theorem, a three–term Capital Asset Pricing Formula which relates the excess rate of return of any risky portfolio to those of three fundamental risky portfolios whose rates of return are pairwise uncorrelated, and a representation suitable for empirical testing.