This synthesis will be of interest to state DOT construction, materials, statistical, specification, and inspection engineers; DOT research staff; pavement construction material suppliers; highway construction contractors; and civil engineering consulting firms, including field and laboratory materials testing personnel. The synthesis describes the state of the practice for defining and measuring variability in highway pavement construction. Data obtained from a review of the literature, a survey of state departments of transportation (DOTs), and discussions with selected state DOT personnel and private materials producers are presented. This report of the Transportation Research Board defines several measures of variability but concentrates on the use of standard deviation as the usual measure of variability. The synthesis updates reported typical variabilities found in materials and construction specifications. Also included are discussions of current research activities as related to variability, how variability can be used in the development of specification limits, the use of incentives and disincentives in specifications, and the need for additional information on the variability of several materials and construction processes.