Unintentional injury is the leading cause of death for children age 1 and older in the United States and is responsible for more child mortality than all diseases combined (Borse et al., 2008). The child injury death rate in the United States ranks as one of the worst among higher income countries and is approximately four times higher than countries with the lowest rates ("Vital Signs," 2012). One in four children annually have an injury that requires medical treatment or results in restricted activity, with an estimated cost of $17 billion per year (Danseco, Miller, & Spicer, 2000; Scheidt et al., 1995). Unlike older children, young children are most likely to be injured in the home where parents and other caregivers are present (Scheidt et al., 1995). As a result, parental supervision has been identified as one of the most important determinants of injury risk for younger children. However, research in this area has focused primarily on the role of mothers in injury prevention, with only a handful of studies examining the role of fathers (Morrongiello, 2005; Morrongiello, Ondejko, & Littlejohn, 2004; Morrongiello & Schell, 2010).Demographic and cultural shifts over the past several decades have tremendously influenced family life in the United States. As mothers have increased their time in the labor force, fathers (particularly married fathers) now spend substantially more time taking care of children than in the past (Pew Research Center, 2013). At the same time, more children are spending time in nontraditional family living arrangements. Because of high rates of marital dissolution, instability within nonmarital relationships, and nonmarital childbearing in the United States (41% in 2010), half of all children will spend some time in a single-parent family (Kennedy & Bumpass, 2008; Martin et al., 2015), and one third of all children will spend time in a family with a biological parent and a residential nonbiological parent (Coleman, Ganong, & Fine, 2000). Because most children continue to live withtheirmothersafterparentalseparation(U.S. Census Bureau, 2012), these statistics suggest that children will be involved with a variety of different "father figures" in their lives, including resident biological fathers, nonresident biological fathers, and mothers' new married or cohabiting partners (from here on referred to as resident social fathers). Very little is known about the role of fathers in child injury risk, and scholars have identified this area as a major gap in the research (Morrongiello & Schwebel, 2008). Given the diversity of children's living arrangements and the importance of injuries in the health profiles of young children, it is important to understand how children's involvement with different types of father figures is associated with injury. In this study we examined the role of resident biological fathers, nonresident biological fathers, and resident social fathers in the risk of injury for children from birth to age 5.Fathers and Child InjuryFathers can be involved with children in many different ways. In this study, we considered three dimensions of father involvement: (a) fathers' residential status vis a vis children, (b) fathers' engagement with children in various activities, and (c) the degree to which fathers cooperate in parenting practices with mothers. Below, we describe the mechanisms through which each of these dimensions of involvement could affect child injuries and suggest how effects could differ by fathers' residential status, biological link to the child, and the child's stage of development.Residential StatusOne of the most basic forms of fathers' involvement is their physical presence in the child's household. As mentioned above, half of children will spend time in a single-parent family, most often with their mother. By definition, children in single-parent families have less access to parental time and material resources than do children in two-parent families (Thomson, Hanson, & McLanahan, 1994; U. …