This paper explains a novel method for the construction of equity indices that offer an efficient risk/return tradeoff. The index construction method goes back to the roots of modern portfolio theory and focuses on the "tangency" portfolio, the portfolio that weights index constituents so as to obtain the highest possible Sharpe Ratio. The major challenge is to generate the required input parameters in a robust manner. The expected excess return of each stock is estimated from portfolio sorts according to the stock’s total downside risk. This estimate uses the economic insight that stocks with higher risk should compensate their holders with higher expected returns. The authors use principal component analysis to extract the common factors driving stock returns and estimate the covariance matrix. They also introduce a procedure to control turnover for implementing the method with low transaction costs.