The delayed entry into marriage that characterizes modern society raises questions about young adults' romantic relationship trajectories and whether patterns found to characterize adolescent romantic relationships persist into young adulthood. The current study traced developmental transitions into and out of romantic relationships from age 18 through age 25 in a sample of 511 young adults. The developmental antecedents of these different romantic relationship experiences in both distal and proximal family and peer domains were also examined. Analyses included both person-oriented and variable-oriented approaches. Findings show 5 distinct clusters varying in timing, duration, and frequency of participation in romantic relationships that range from those who had only recently entered into a romantic relationship to those who had been in the same relationship from age 18 to age 25. These relationship outcome trajectory clusters were predicted by variations in competence in early relationships with family and peers. Interpersonal experiences in family and peer contexts in early childhood through adolescence thus may form a scaffold on which later competence in romantic relationships develops. Findings shed light on both normative and nonnormative developmental transitions of romantic relationships in young adulthood.