Inheritance is the ability to build new classes from existing classes. The new class is defined as a subclass of another class, called its superclass. A subclass inherits from its superclass the mandatory and optional attributes and its structural parent classes in the directory hierarchy. All classes are subclasses, directly or indirectly, of a single abstract object class, called top. In Active Directory, a class has exactly one superclass; top is its own superclass. An ordered set of superclasses of a class, ending with class top, is its superclass chain ([X501]). The superclass chain of a class does not include the class itself, except that the superclass chain of top is the single-element sequence [ top ].

Abstract classes can inherit only from abstract classes, auxiliary classes can inherit from all classes except structural classes, and structural classes can inherit from all classes except auxiliary classes. Classes of the category 88 class (section can inherit from all classes.