Modern insert systems have been available on the dental market since the late 1980s. In general, two major systems can be distinguished: those with and those without preparation instruments in combination with matching standardized inserts. It is claimed that one of the advantages of insert systems is the better marginal adaptation of insert/composite restorations compared to mere composite restorations: the integration of inserts reduces the polymerization shrinkage stress and lowers the overall coefficient of thermal expansion. In vitro data indicate that adapting the insert size to the most precise fit produces a quality of marginal adaptation comparable to that of ceramic inlays. Inserts also facilitate the establishment of a proximal contact. With respect to wear, no significant differences are detected between composite and insert restorations. The bond between insert and composite is susceptible to contamination during operative procedures. Short-term clinical investigations confirm in vitro findings regarding improved marginal adaptation and increased wear resistance. Long-term controlled clinical studies are in progress, but data are not yet available. Based upon the present in vitro and in vivo data it can be concluded that the insert technology shows promising results, but further investigations regarding, for example, stability of the insert/composite bond, fracture resistance of the overall restoration, and wear behavior are necessary to predict the clinical success of this alternative restoration procedure.