Courts have the power to modify child custody arrangements to meet the needs of the child and to respond to changes in the parents’ lives.

A parent seeking to change custody through the court usually must show that the conditions have changed substantially since the last custody order. The change of circumstance usually involves something negative in the child’s current environment–such as improper supervision, or harmful conflicts with the custodial parent or stepparent.

A child’s preference to live with the noncustodial parent can be a basis for modifying custody, but the child’s reasons must be well-based and not appear to be the result of coaching or bribery.

In one case, a father was trying to gain custody of his thirteen-year-old son. In the days before the custody hearing, the father presented his son with a series of gifts reminiscent of the song "The Twelve Days of Christmas". Among the acquisitions of the boy: a horse, two television sets, a minibike, a shotgun, a motorcycle, and a private telephone. The father did not gain custody.

In addition to showing a change in circumstances, the parent seeking a change of custody must show that he or she can provide a better environment for the child than the child’s current environment.

In order to discourage parents from constantly litigating custody, some states apply a special standard for custody modifications sought within the first year or two after a prior custody order. In those states, the parent must show not only a change of circumstances, but also that the child is endangered by the child’s current environment. After expiration of the one- or two-year period, the courts apply normal standards for modification (without having to show endangerment).

If parents voluntarily wish to change custody or the visitation schedule (see below), they may do so without having to prove special factors such as endangerment or a change in circumstances. Parents may change custody and visitation without obtaining a court order, but if the parent receiving custody or more visitation wants to make the modification "official"–thus making it more difficult for the other parent to go back to the old system–it is best to obtain a court order modifying custody and visitation.

In addition, an informal change of custody will not necessarily stop a parent’s support obligation–only a court order can provide certainty of that.