Commission 40 of the International Astronomical Union has adopted a new longitude system for Jupiter, labelled System III(1965), to replace the provisional System III (1957.0). The specification of the prime meridian and epoch for the new system differs slightly from that recently published. Its rotation rate implies a period of 9h55m29s.711¿0s.04, consistent with recent determinations from decimetric and decametric data. For both the new and older systems, equations are provided which are useful in the evaluation of longitudes for the analysis of Jupiter radio, particle and field data from Earth and spacecraft observations.