Child custody presumptions have formed part of Anglo-American law for centuries. Both the paternal preference rule at common law and the tender years doctrine that supplanted it in the nineteenth century signaled the law's conviction that custody was indivisible: after a marital breakup, children could be entrusted to only one parent, with the other an infrequent visitor. This “rule of one” began to weaken in the last third of the twentieth century, as the movement toward gender equality called attention to the importance of both parents in the care and nurturance of children and loosened the link between gender and parenting role. Left without a presumption to direct their custody deliberations, courts turned—often by legislative fiat—to the more inclusive but less definitive best interests standard. Although sole custody decrees were still the norm, some courts began to see in joint custody an opportunity for a child to continue a strong and meaningful relationship with both parents. Courts, legislatures, and commentators are changing the vocabulary of child custody to reflect the evolving reality of twenty-first century family life. Parental responsibilities after separation or divorce are increasingly referred to as “decision-making” instead of “legal custody” and as “parenting time” in lieu of “physical custody.” Calls for a 50/50 joint parenting time/physical custody presumption have sparked controversy. In some states, legislation already aims to ensure frequent and continuing parent–child contact with no specific temporal sharing formula. But putting any of these presumptions into effect in light of the statutory “best interests” concerns make the court's task—absent parental agreement—extremely complex. The interplay of domestic violence and “friendly parent” provisions with joint custody presumptions pose another array of complicating factors. Context is critical in assessing these statutory choices, on which no consensus currently exists. The task now is to avoid using the hard edge of legal presumptions to undermine the lived experience of children, while at the same time circumventing the perils of unpredictable case-by-case determinations unguided by presumptions or preferences. The most promising efforts chart a third course: nudging separating and divorcing parents into a framework that encourages them to implement shared parenting. Shifting the parental focus from litigating custody to jointly crafting a parenting plan also may serve to alleviate the worst aspects of the trauma children often experience when their parents break up.Key Points for the Family Court Community:Until recently, child custody presumptions adhered to a “rule of one”: courts generally insisted that only one parent could properly be awarded child custody.Child custody law is moving toward a norm of shared parenting, with frequent and continuing contact provided for each parent.Legal terminology is also shifting to encourage collaborative parenting. “Decision-making” is replacing “legal custody,” and “physical custody” is giving way to “parenting time.”A legal presumption of joint custody may mean no more than a generalized shared parenting arrangement, but applying the emerging statutes and case law to award joint custody can involve a quite complex determination process.Shifting the parental focus from litigating custody to implementing a shared parenting plan may avoid the pitfalls of litigating under the “best interests” standard either with or without a legal presumption.