This paper reports trends in educational assortative marriage from 1940 to 2003 in the United States. Analyses of census and Current Population Survey data show that educational homogamy decreased from 1940 to 1960 but increased from 1960 to 2003. From 1960 to the early 1970s, increases in educational homogamy were generated by decreasing intermarriage among groups of relatively well-educated persons. College graduates, in particular, were increasingly likely to marry each other rather than those with less education. Beginning in the early 1970s, however, continued increases in the odds of educational homogamy were generated by decreases in intermarriage at both ends of the education distribution. Most striking is the decline in the odds that those with very low levels of education marry up. Intermarriage between college graduates and those with "some college" continued to decline but at a more gradual pace. As intermarriage declined at the extremes of the education distribution, intermarriage among those in the middle portion of the distribution increased. These trends, which are similar for a broad cross section of married couples and for newlyweds, are consistent with a growing social divide between those with very low levels of education and those with more education in the United States.