To improve the quality and stability of couple and father-child relationships in fragile families, researchers are beginning to consider how to tailor existing couple-relationship and father-involvement interventions, which are now targeted on married couples, to the specific needs of unwed couples in fragile families. The goal, explain Philip Cowan, Carolyn Pape Cowan, and Virginia Knox, is to provide a more supportive developmental context for mothers, fathers, and, especially, the children in fragile families. The authors present a conceptual model to explain why couple-relationship and father-involvement interventions developed for middle- and low-income married couples might be expected to provide benefits for children of unmarried parents. Then they summarize the extensive research on existing couple-relationship and father-involvement interventions, noting that only a few of the programs for couples and a handful of fatherhood programs have been systematically evaluated. Of those that have been evaluated, few have included unmarried couples as participants, and none has investigated whether interventions may have different effects when unmarried fathers live with or apart from the child. Furthermore, although the funders and creators of most programs for couples or for fathers justify their offerings in terms of potential benefits for children, the authors note that the programs rarely assess child outcomes systematically. Next, the authors consider whether interventions for working-class or middle-class fathers or couples that have shown benefits for family members and their relationships might be helpful to fragile families, in which the parents are not married at the time of their child's birth. Because evidence suggests that couple-oriented programs also have a positive effect on father involvement, the authors recommend integrating couple and fatherhood interventions to increase their power to reduce the risks and enhance the protective factors for children's development and well-being. The authors emphasize the need for more research on program development to understand the most effective ways to strengthen co-parenting by couples who are the biological parents of a child but who have relatively tenuous, or already dissolved, relationships with one another. In closing, the authors summarize how far the family-strengthening field has come and offer suggestions for where it might go from here to be helpful to fragile families. (Contains 4 tables and 50 endnotes.)