According to Dr. Reena Sommer, a divorce and custody consultant with expertise in high conflict divorce and custody disputes, the number of contested custody cases has steadily risen in most western countries since the mid-1980s because courts recognize that "joint custody" is the preferable way for rearing children of divorced families. For most of the twentieth century, sole physical custody almost always went to mothers; the financial responsibility of paying children support almost always resting on the fathers. In this regime, specified access arrangements made maintenance of a relationship with children very difficult.

Over the years, judges and clinicians have used several conceptual models to guide them in child custody disputes. The "tender years" presumption held that young children should be with their mothers. This presumption reflected an awareness of children as unique human beings rather than simply small adults. It also emphasized the importance of the maternal-infant relationship, and survived well into the twentieth century. Another conceptual model is called the "least detrimental alternative," a presumption that holds that courts and clinicians should be guided by the more realistic notion that all children in separating or divorcing families are harmed to some extent. The goal is to find the solution that appears to harm them the least.

In the 1970s, courts moved toward the idea of joint custody. The intent of the new divorce routine was to place the responsibility for caring for children physically, emotionally and financially on both parents, not just one. In some cases, both parents did not accept the idea that the best interests of children would be served by having both parents in their lives. The linch-pin appeared to be the recognition that post divorce financial support was no longer the domain of the noncustodial parent and was instead a shared responsibility. Suddenly, there were financial incentives for both mothers and fathers to oppose joint custody. For mothers, the incentive was to hold onto child support; for fathers it was not to pay it.

So out of this dilemma, a whole new legal challenge emerged - the contested custody case, and more of them, due to that increasing number, being litigated. Sometimes parents resolve custody and visitation by themselves or with mediation, but often a custody battle takes shape that turns the end of the marriage into trench warfare and results in custody evaluation. There is much work for those clinicians, since approximately one in two marriages in the United States ends in divorce, which affects about a million children per year. About 10 percent of these divorces involve custody litigation.

Courts find deciding contested custody cases very challenging because judges know virtually nothing about the parents. Judges are generally ill equipped to make decisions about which of the two warring parents are best able to provide for their children. Given these circumstances, the most logical solution seems to be having a professional who had expertise in the areas of child development, family dynamics and psychopathology to evaluate the family members and then make recommendations to the court about custody and access. Hence, the custody evaluation and the custody evaluator.