Data from the Intergenerational Panel Study of Parents and Children are used to identify the influences of adult union transitions on changes in attitudes toward cohabitation among a sample of 794 young adults. The analysis examines the extent to which attitudes about cohabitation change as a result of entry into and exit from cohabitation and marriage. A dynamic interpretation of union transitions is formulated, and results demonstrate that entry into a first cohabitation and divorce after direct entry into marriage are associated with increasingly positive attitudes toward cohabitation between the ages of 18 and 31. Some evidence suggests that direct entry into stable marriage leads young adults to view cohabitation less favorably.