Flexible risers have been used in many applications for several years now. The design of a flexible riser configuration in the first years was based on quasi-static calculations. At present the designer is supported with enhanced simulation software tools. For this purpose discrete element methods have been developed. Results from full scale measurements have indicated that the modelling of hydrodynamics and mechanical properties should be subjected to further research. This is not only relevant for extreme sea state analysis but also for fatigue analysis. Improved fluid load models have been derived from systematic model tests with full scale riser sections. Modelling of material damping and non-linear bending stiffness with hysteresis effects proved to be of significant importance.