Prior studies find that a strategy that buys high-beta stocks and sells low-beta stocks has a significantly negative unconditional capital asset pricing model (CAPM) alpha, such that it appears to pay to "bet against beta." We show, however, that the conditional beta for the high-minus-low beta portfolio covaries negatively with the equity premium and positively with market volatility. As a result, the unconditional alpha is a downward-biased estimate of the true alpha. We model the conditional market risk for beta-sorted portfolios using instrumental variables methods and find that the conditional CAPM resolves the beta anomaly.THE SHARPE-LINTNER CAPITAL asset pricing model (CAPM) implies that exposure to market risk, as measured by beta, should be compensated by the market risk premium. Based on the performance of portfolios formed on lagged firm-level beta, however, a number of empirical studies find that the riskreward relation is too flat. For example, Friend and Blume (1970) and Black, Jensen, and Scholes (1972) demonstrate that portfolios of high-beta stocks earn lower returns than implied by the CAPM and therefore have negative alphas, whereas portfolios of low-beta stocks earn positive alphas. French (1992, 2006) extend these results by showing that the beta-return relation becomes even flatter after controlling for size and book-to-market characteristics. Finally, Frazzini and Pedersen (2014) confirm the underperformance of highbeta stocks over a long sample period extending from 1926 to 2012 and develop a "betting-against-beta" strategy, which has drawn substantial interest from academics and practitioners alike. 1 * Scott Cederburg is with the Eller College of Management, University of Arizona. Michael O'Doherty is with the Trulaske College of Business, University of Missouri. We are grateful to Phil Davies and Rick Sias for their detailed suggestions on the paper. We also thank 737 738The Journal of Finance R Figure 1. Cross-sectional distribution of firm betas, July 1927 to December 2012. The figure displays statistics for the cross-sectional distribution of firm betas. The dashed line is the median and the solid lines show the 5 th and 95 th percentiles of firm betas. Firm betas are estimated at the beginning of each month using daily returns over the previous 12 months.