Many techniques have been described in the literature to assess the durability of dental restorative materials in vivo. This paper reviews the literature with particular emphasis upon the assessment of the wear resistance of posterior composite resins. A recent American Dental Association (ADA) publication established a number of additional requirements to specification ADA 27. In particular, it suggests that a wear rate of less than 50 μm per year is desirable in such posterior composites. In this review, both the subjective and objective methods for assessment of wear are discussed, and the relative advantages and disadvantages outlined. It appears that there is no single in-vivo method which currently gives a full impression of long term in-vivo durability. This paper therefore suggests that clinical trials to monitor durability should be of several years' duration; qualitative assessment should be used to provide an overall clinical impression but quantitative assessment should also be used to highlight significant differences which are not readily detected by subjective ranking methods.