This article examines the prevalence, predictors and outcomes of unmarried mothers’ repartnering patterns following a nonmarital birth. Results indicate that, within five years after a birth, approximately two-thirds of unmarried mothers end their relationship with the focal child’s biological father, and more than half of these mothers enter new partnerships. Among those who repartnered, 60 percent of mothers formed unions with men who had higher economic capabilities than their former partners, 20 percent formed unions with men of similar capabilities, and 20 percent formed unions with men who had lower capabilities. This pattern holds for both nonresidential and coresidential unions. Our findings are consistent with marriage market, learning and evolutionary biology theories about union formation, and they provide support for qualitative evidence that unmarried mothers have high standards for new partners. While many mothers find new partners who seem to offer a higher level of economic security, many other mothers remain unpartnered, likely due (at least in part) to the limited pool of potential partners with relatively high levels of economic promise.