The invention relates to an offshore vessel mooring and riser inboarding system, and to an associated method. In an embodiment of the invention, an offshore vessel mooring and riser inboarding system (10) is disclosed. The system comprises a support assembly (16) mounted on a vessel such as an FPSO (12); a first mooring portion (20) located in an offshore environment and moored such that rotation of the first mooring portion is restricted; a second mooring portion (28) rotatably coupled to the first mooring portion and secured to the support assembly for rotation therewith relative to the first mooring portion; a plurality of risers (30a, 30b, 30c) coupled to the second mooring portion such that the risers can twist together on rotation of the second mooring portion relative to the first mooring portion; and a rotatable coupling (32a, 32b, 32c) associated with each riser and by which the risers are coupled to the second mooring portion, to thereby facilitate rotation of the risers relative to the second mooring portion.