Court rules allow a qualified expert to render an opinion addressing the ultimate issue to be decided by the Court. Thus, psychologists routinely recommend custody of minor children to one, the other or jointly. There are no formal requirements to qualify as an expert other than a demonstration to the Court of education, training and skills in the area of expertise. The issue of custody can be multifaceted which lends itself to varying expert opinions. Preferring one parent over the other may vary with regard to the issues of parenting skills, abuse or neglect, violence and/or temperament, supervisory skills, education development, health, work schedule and environment.

The psychological expert may be retained by one parent, retained by both parents, or appointed by the Court. Most therapists prefer to be appointed by the Court to maintain their neutrality and avoid the practical difficulties of rendering an opinion not favorable to the client. Cost is often a factor. Allocating the cost of one expert is often a motivating factor.