This paper attempts to identify the principal parameters that influence the behavior of drilling and production risers and to explain how and why they do so. Clear understanding of these influences enable particular risers to be optimized rapidly without recourse to an inordinate number of computer analyses. The points of greatest concern, to the riser designer, are: stress levels in the main length of riser; angular movement at sea bed (or moment, if the connection is rigid); relative movement at riser/platform connection. The approach used in the paper has been to derive analytical expressions, for simplified riser cases. Conclusions drawn from these expressions have then been checked for validity, by using a dynamic analysis computer program to simulate a wide range of cases.