This synthesis will be of interest to research, specifications, materials, design, and construction engineers; contract and specification administrators; agency project managers and staff; and concrete bridge deck construction contractors. This synthesis describes the state of the practice with respect to the development and present status of waterproofing membranes for concrete bridge decks. This report of the Transportation Research Board describes the use of waterproofing systems applied to new bridge decks and the rehabilitation of deteriorated concrete bridge decks. In addition, this synthesis describes current practice with regard to methods for assessing the effectiveness of membranes, criteria for use, installation practices, and factors that affect the performance of waterproofing systems in new construction and rehabilitation. Suggestions for future research are also included.