Responsible co-parenting—a process in which fathers and mothers work together effectively in their role as parents regardless of the nature of their personal relationship—is integral to the well-being of children. When parents collaborate, support each other, and share goals and beliefs about their children, fathers are more involved in their children’s lives. But a new qualitative study by Mathematica Policy Research reveals that about 7 in 10 fathers who participated in in-depth interviews for the Parents and Children Together (PACT) evaluation are in co-parenting relationships that are marked by either frequent conflict or little to no communication between the parents. This finding, along with others from the qualitative component of the PACT evaluation, helps us understand the complex challenges fathers face in attempting to co-parent their children.