Clinical evaluation of restoration acceptability includes marginal adaptation, restoration and preservation of anatomic form, color match, cavosurface discoloration, and presence of marginal caries. This paper will review what is known about marginal fit of all materials relative to their acceptable fit. Some explanation will be given of how material properties affect marginal fit, what the expected longevity of different materials is relative to marginal fit, and how marginal fit affects development of secondary or marginal caries. Marginal fit is assumed to affect restoration longevity by either encouraging or discouraging microleakage and development of secondary or marginal caries. Marginal fit and its effect on the health of the gingival tissues have been reviewed in an earlier paper on polishing and will not be reviewed here. Is there some correlation between marginal fit of the various materials used in restorative dentistry and this assumption? This paper will review the literature found on Medline and present the science behind the clinical significance of marginal fit utilizing in vitro studies where necessary and in vivo studies whenever possible. Numerous authors replicating these studies are used to improve reliability and replicability.