The requirements for waterproofing materials have been studied, both in the Laboratory and on bridge sites, against requirements for adhesion, stability and thermal properties. Laboratory experiments to evaluate the resistance of the membrane system to substrate cracking and damage, by constructional work, at 10 degrees and 20 degrees Celcius have been developed and standards of performance proposed. The problems of protection of the membrane against damage and of blistering are considered. Close liaison with the industry had led to the development of an increased range of materials, both of prefabricated and applied in situ types, more suited to their working environment. A survey of over 30 bridges, in service for about eight years, has shown that waterproofing is generally satisfactory, but leakage can still occur through areas such as expansion joints. The importance of attention to the details of the waterproofing system and of good workmanship is emphasised