I assess whether intermarriage between Protestants and Catholics has increased over the course of the twentieth century and, if it has, whether the declining salience of religious boundaries has been accompanied by a rising importance of educational boundaries in spouse selection. By analyzing a set of national surveys that were conducted between 1955 and 1989 and using a research design that separates the effects of period and duration of marriage, I examine changes over a longer period of time than any previous study has done. Multivariate loglinear analyses show that intermarriage between Protestants and Catholics has increased dramatically since the 1920s, while intermarriage between different educational groups has decreased. Currently, the social boundaries that separate educational groups seem to be stronger than the boundaries that separate Protestants and Catholics. In addition, there is some evidence that interfaith marriages have become increasingly homogamous with respect to education, suggesting that education has replaced religion as afactor in spouse selection.