As is now quite well known and documented, cablestayed bridges around the world are commonly exhibiting excessive and unanticipated vibrations of the main stays, often associated with the simultaneous occurrence of wind and rain. These largeamplitude vibrations are of concern because they induce undue stresses and fatigue in the cables themselves and in the connections at the bridge deck and tower. As such instances continue to be reported, their mitigation has become a significant consideration in cable-stayed bridge design and for retrofit of existing structures. Until fully resolved, this issue potentially threatens the widespread acceptance of this attractive and economical form of bridge structure. The current understanding of the nature of these