Judges on a tier below a decision are bound by the higher court's ruling. This is mandatory precedent. Judges on the same tier are not strictly bound, but in t

Judges on a tier below a decision are bound by the higher court's ruling. This is mandatory precedent. Judges on the same tier are not strictly bound, but in the interest of consistency (the law always seeks to be applied in the same way to the same situation), will look to the rulings of other courts on their level if no higher court has ruled. This is called persuasive precedent. The Supremes often take a case because the lower courts, (Circuit Courts of Appeals) have ruled differently on the same issue. This is called a circuit split.