It has been well established that composite resin restorations have leakage at the margins. The polymerization shrinkage of the material and its inadequate adhesion to the cavity walls are the primary causes. Unlike silver amalgam restorations, which are self-sealing with age, the gap at the composite-to-tooth interface tends to persist and invite postoperative sensitivity, adverse pulp reactions, and the development of recurrent caries. Many techniques or materials have been advocated to improve the clinical adaptation of this material and to reduce marginal leakage. They limit the effect of polymerization shrinkage and/or enhance the bonding of the composite material to the tooth structure. This article reviews the clinical techniques and materials that have been suggested and are presently available to improve the marginal quality of composite resins, with special reference to posterior restorations.