The purpose of this paper is to exhibit existing replacement models and to develop new replacement models for managing equipments in large organizations, private or public. Some of the models in this paper are well known and in use, and some are not. All these models are classified, depending on main factors which play key roles on the models. One group is the models in which the economic factor plays a key role, and the other is those in which both the economic factor and the effectiveness factor play key roles.