Two long-term shift s in the family have remade family law in the United States. One involves the fight of same-sex families for recognition. Barred access to marriage and in many jurisdictions to adoption and other forms of family status, same-sex couples have fought for the expanded use of contract and sometimes newly created statuses to forge families of choice. During the same period, different-sex couples have also forged new types of families as marriage has become optional, and as adults join together, have children, separate, and form new relationships. The courts have responded to these two developments through the use of different doctrines, sometimes extending, for example, domestic partnerships and civil unions solely to partners who could not marry, or sometimes interpreting equitable principles to recognise same-sex partners without a biological tie as parents of a child while addressing the parental standing of traditional step-parents through a different set of legal doctrines.

This chapter examines recent developments in US family law and argues that the time for convergence among these different legal doctrines is at hand. Three developments in particular may drive that convergence. The first is the ability of same-sex couples to marry. This raises the issue of whether marriage will become a bright-line marker between committed couples and those in more contingent relationships and, if so, what the consequences will be. Determining what the marital presumption of paternity means in the new era may be a particularly important aspect of that process, and it may signal the degree to which doctrines based on marriage and doctrines based on parentage by intent converge into a single set of precepts that establish responsibility for children at the time of birth.

The second involves the continuing role of functional parentage. The inability of same-sex couples to gain recognition for their relationships helped spur recognition of parentage by estoppel, de facto parentage, psychological parentage, and other doctrines establishing parentage rights and obligations on the basis of the assumption of parental roles. The extension of these doctrines to step-parents and uncommitted partners, however, does not necessarily have the same meaning as application of the same doctrines to same-sex couples who could not marry, but who nonetheless constituted the only two parents a child was likely to have directly involved in her life.