This analysis examines trends in young adults in union formation comparing trends in marriage to trends when cohabitation is included as well as marriage. It then documents the characteristics of cohabiting couples in terms of the duration of the union presence of children perceived stability marriage plans and opinions about cohabitation. Finally it analyzes several marriage-related attitude items among all unmarried persons under age 35. The US National Survey of Families and Households provides data on a national sample of 13017 respondents. The large increases in the proportion never married among persons in their early 20s is commonly interpreted to mean that young people are staying single longer. Because of cohabitation however being unmarried is not synonymous with being single. Young people are setting up housekeeping with partners of the opposite sex at almost as early an age as they did before marriage rates declined. 3/4 of the decline in the proportion of women married by age 25 was offset by increased cohabitation. The role of cohabitation in replacing early marriage is most pronounced for persons who have not completed high school. Cohabiting relationships tend to have been formed recently although 1 in 5 have been cohabiting for 5 years or more. Most cohabitors expect to marry their partner although there is a surprisingly high level of disagreement among partners about this.