This paper uses multiple data sources and a unified methodology to estimate the trends and levels of the U.S. high school graduation rate. Correcting for important biases that plague previous calculations, we establish that (1) the true high school graduation rate is substantially lower than the official rate issued by the National Center for Educational Statistics; (2) it has been declining over the past 40 years; (3) majority/minority graduation rate differentials are substantial and have not converged over the past 35 years; (4) the decline in high school graduation rates occurs among native populations and is not solely a consequence of increasing proportions of immigrants and minorities in American society; (5) the decline in high school graduation explains part of the recent slowdown in college attendance; and (6) the pattern of the decline of high school graduation rates by gender helps to explain the recent increase in male-female college attendance gaps.