At the turn of the 21st century, the American Law Institute, after over a decade of work, released its "Principles of Family Dissolution." Unlike other releases by that body, it was not a Restatement of the Law but a recommendation of "best practices"—what the law should be. It recognizes that judges are ill-suited to make custody determinations on their own and offers recommendations for change.

In Chapter 2, it proposes a presumption of joint custody in decision making and a sharing of time in proportion to the amount of time each parent spent caring for the child prior to the separation, called the Approximation Rule.