Shifts in union formation and childbearing have undoubtedly altered the prevalence and structure of higher-order unions and stepfamilies, but no study has examined trends over time. Comparing the 1988 and 2011-2013 cycles of the National Survey of Family Growth, I produce estimates of repartnering and stepfamily formation among currently partnered women aged 15 to 44 years. The percentage of intact unions that are remarriages stayed stable (around 27% to 28%), but a growing proportion of currently married and cohabiting women had another cohabiting partner in the past. The percentage of intact unions that are stepfamilies increased from 24% to 31%, with an increase in cohabiting stepfamilies from 19% to 39% of all stepfamilies. Furthermore, while the majority of remarriages are stepfamilies, the majority of women’s stepfamilies are no longer remarriages due to union formation among never-married parents. Cohabiting (but not marital) stepfamilies also exhibited changes in which partner had children and in shared childbearing.