Successful viral infection depends on the virus capacity to evade the hosta interferon (IFN)-mediated innate immune response, and thereby prevent the establishment in cells of an antiviral state. Viral evasion of IFN immunity is mediated by multifunctional, virus-encoded IFN-antagonist proteins, which interact with diverse host factors, including intracellular signalling and effector molecules of the IFN system; thus, IFN-antagonists represent potential targets for antiviral therapies, but the molecular events underlying their functions are currently poorly defined.Using live-cell imaging, molecular/cell biology and reverse genetics approaches with animal infection models, we have investigated the functions of the archetypal IFN-antagonist, rabies virus P protein, finding that it undergoes intricately regulated subcellular trafficking involving numerous sequences for interaction with the host cella nuclear transport machinery, cytoskeletal components, and IFN signalling/effector molecules. Through these interactions, P-protein undergoes highly regulated nucleocytoplasmic trafficking to target host factors in specific subcellular sites, and thereby regulate the trafficking/functions of components of the IFN system by several novel mechanisms. Our in vivo studies have shown that P-protein trafficking is a vital component of immune evasion and pathogenicity, the first such demonstration for any virus; importantly we found that mutations affecting P-protein interactions with cellular trafficking machinery can specifically attenuate virus in vivo. This work identifies IFN-antagonist subcellular trafficking/interactions as vital components in virulence, and potential therapeutic targets. IFN-antagonist trafficking has been reported for numerous human pathogenic viruses, including Nipah/Hendra, measles and Dengue, indicating that it may represent a common target for therapies for a number of highly virulent/lethal human diseases.