No restorative material presently available is as good as supported tooth structure and it is unlikely that a usable dental restorative material with the physical properties of enamel will ever be developed. The purpose of cavity preparation is to remove carious material and preserve sound tooth structure. Any additional removal of tooth structure is necessary for the convenience of the operator or because of limitations of the restorative materials. Presently available esthetic restorative systems for nonfunctional areas and selected anterior functional areas allow for designing cavity preparations where the only two considerations are removal of caries (and unsupported enamel) and placement of retentive features. The problem of cavity design for restoration of functional surfaces is not answered easily, but there is reasonable hope that in the near future an esthetic restorative material will be available that has the strength and other necessary properties to serve in functional areas. There should be no specific "ideal" design for cavity preparation. Each defect should be custom designed to remove the caries or defect and perform the additional steps necessitated by the limitations of the operator or restorative material. As advocated by Black in one of his later publications, it is necessary to make mouth-by-mouth and tooth-by-tooth judgements concerning the most desirable outline form to be obtained.