During construction and for the first year of operation of the second Severn crossing, the dynamic response of the cable-stayed section of the structure was monitored. This gave valuable insight into the dynamic behaviour of cable-stayed bridges in different wind conditions at various stages of construction. The opportunity was also taken to develop and test a remote computer vision displacement measurement system. The actual behaviour was compared with predictions from wind tunnel tests and from a finite element model. Following problems with cable oscillations during construction, cable damping parameters were measured and an effective secondary cable system was installed to prevent the vibrations occurring. (A)