We examine family systems and family relationships. Using family systems theory (Cox & Paley, 1997, 2003; Minuchin, 1985), we focus on how families are viewed as a hierarchically organized system, comprised of smaller relationships (i.e., subsystems) such as parent–child relationships, embedded within larger systems such as extended families and their broader social ties. We organized the discussion of subsystems as follows: (a) Core subsystems, including relationships of romantic partners, coparenting alliance, parent–children, and siblings; and (b) Subsystems with broader social ties, in the form of extended family and/or intergenerational ties, including coparenting alliances in post-divorce or foster families as well as parents and parents-in-law relationships. We also consider these various subsystems within and across diverse families and family contexts, attending to aspects of gender, family structures, income, sexual orientation, race/ethnicity, cultures, and national origins. We end with suggestions for future research (e.g., combining the lenses of family systems with intersectionality).