The establishment and development of composite resins has led to their use as a posterior restorative material. Although posterior composites have evolved considerably, both clinical studies and experience have confirmed that several problems still remain concerning their clinical properties and the relative complexity of handling the material. In order to resolve these problems, two different manufacturers have introduced composite resin systems for the fabrication of direct or indirect resin inlays and onlays which are cemented into the acid-etched preparation with a modified composite resin. Both systems are based on the same concept: the polymerization of the resin takes place out of the mouth in a special oven where a specific heat-curing procedure is followed. There is an essential difference between the two systems. When the direct resin system is used, the inlay is formed and partly light-cured into the tooth preparation, then it is removed for further polymerization. When the indirect system is used the procedure takes place in the lab where the inlay is formed on the die. This article presents both systems, the step-by-step procedure that has been followed in several clinical cases as well as their advantages and disadvantages.