Traditionally synthetic fiber ropes based on nylon and polyester fibers have been widely used in the marine industry. In recent years, as the offshore petroleum industry has moved to depths beyond 1000 meters, these have attracted more attention for both mooring and deep sea handling, and high performance ropes (high modulus polyethylenes (HMPE), aramids) are also being studied. Ocean energy converters will also require mooring systems with long term reliability. Following pioneering work by Petrobras large polyester fiber ropes are now being used in station keeping of floating platforms off Brazil and in the Gulf of Mexico [1]. This application followed extensive development projects and sea trials, and has resulted in a large database of tensile properties. Tension is clearly the dominant loading in most marine applications but torsion and flexure may also be present. Torsion can be induced during tension loading, due to the unbalanced construction of some ropes (e.g. 6+1 wire ropes). However, even in a balanced construction, the movement of an adjacent unbalanced steel wire loaded in tension may introduce twist. Torsion may also arise during handling or installation operations. Bending occurs whenever ropes pass over pulleys, and can rapidly degrade high performance ropes. A thorough understanding of all these phenomena is therefore essential for safe design.