A "604b" is a custody evaluation that is sometimes used by Illinois courts in divorce and custody cases. It gets its name from the section of the law that it comes from: section 750 ILCS 5/604(b) of the Illinois Marriage and Dissolution of Marriage Act. 604b evaulations are not used in every custody case but may sometimes be required when the judge or a party feels that a mental health professional should be appointed to advise the court in connection with the custody dispute. This goes beyond what a Guardian Ad Litem (G.A.L.) will normally do as the 604b evaluator will typically conduct psychological testing, something that attorney-G.A.L's cannot do. 604b evaluators will also spend a time getting to know the parents and the children involved and may also speak with other sources (other family members, teachers, live-ins, etc).