A sample of 443,520 married couples from the 1970 U.S. Census is examined to determine trends and variations in educational homogamy and husband-hypogamy, partially replicating a study from the 1960 Census. Assortative mating by education has implications for both social differentiation and marriage patterns. Educationally homogamous marriages are now occurring at levels higher than expected by chance but lower than would occur if equality of education were determinate in mate selection. However, levels of homogamy remain lower than at the beginning of the century. Change in educational homogamy from cohort to cohort is strongly related to change in the educational distributions of husbands and wives. A trend for white women in heterogamous marriages to marry up in education is also related to change in the relative education of men and women. Education remains a major factor in mate selection, a major discriminating characteristic in American society, and potentially a major source of differences in marital patterns.