The implications of family structure for child well-being have been a central topic of research for several decades. In its simplest form, it is the comparison between two-parent and one-parent families that is the root of concern for child well-being. Children who live with two married parents are defined in most government statistics as living in two-parent families, whereas children who live with just one biological parent due to death, divorce, or having never married have been considered to live in single-parent families. However, the issue is much more complex, and trends in family structure among American children over recent decades make it increasingly necessary to specify the biological and social relationships between children and the adults in their lives in order to understand the implications for child well-being.