Microfilled resins generally have physical properties inferior to those of conventional composites. A lower in organic filler content or higher polymer/filled ratio results in a lower modulus of elasticity, greater thermal dimensional change, less resistance to indentation and abrasion, and greater water sorption. The ability to finish and to maintain a smooth surface texture is a major advantage, although it has not been proved clinically that microfilled resin restorations result in less plaque adherence nor do they enhance soft tissue response. Early clinical trials, after two to three years in vivo, indicate a greater wear resistance for these materials than for conventional composites. At this time, current evidence suggests that a decrease in filler particles size to less than 1 micrometer and a lower filler loading of the resin matrix permit the clinical development and maintenance of a smooth surface texture on restoration surfaces. There is no published evidence that the decrease in many of the physical properties leads to early signs of clinical deterioration and failure. In vivo studies extended for longer periods are necessary to make a knowledgeable judgment on the true clinical value of these composites. A classification system for composite restorative resins is being prepared by the Council on Dental Materials, Instruments, and Equipment. It will be published in a future issue of The Journal.