A mooring system, and connector assembly, which in a preferred embodiment is a vessel mooring and fluid transfer system. The connector assembly has a first portion (2A) configured to be coupled to one or more mooring lines (1), and a second portion (2B) configured to be coupled to a vessel. The first and second portions are rotatable with respect to one another to permit a vessel coupling on the second portion to swivel about the mooring coupling on the first portion. In a preferred embodiment, the connector assembly comprises a guide (2E) for a conduit, which may be a fluid transfer conduit such as flexible riser (6). The invention also provides methods of use of the mooring systems described.