Nonmarital childbearing has increased dramatically in the United States since the early 1960s, rising from 6% of all births in 1960 to 41% in 2008 (Hamilton, Martin, & Ventura, 2010). Whereas similar trends have occurred in many developed nations, the United States stands out in the extent to which such births are associated with socioeconomic disadvantage and relationship instability. This has given rise to a new term, fragile families, which we define as unmarried couples who have a child together. The increase in fragile families reflects changes not only in the initial context of births but also in the fundamental nature and patterns of child rearing. Although much of the recent literature on coparenting has focused on married, coresident parents with children, most unmarried couples will break up within only a few years of a new child’s birth (McLanahan, 2009). Therefore, for many unmarried parents, coparenting will occur across households and may be more similar to coparenting among divorced parents than among married parents. However, given the disadvantaged characteristics of unmarried parents, coparenting in this context may be even more complicated than it is after a legal divorce. In this chapter, we provide an overview of coparenting in fragile families, focusing particularly on what has been learned from the Fragile Families and Child Wellbeing Study. We begin by identifying key theoretical perspectives related to coparenting generally. Then, we briefly describe the typical characteristics of unmarried parents with children and the nature of their couple relationships over time. Next, we summarize contributions to the coparenting literature from more recent studies focused on unmarried parents (or similar populations), and we present some new data about coparenting among fragile families. Finally, we conclude by suggesting key areas for future research and noting implications for public policy.