In this special issue we aim to review replicating competent reporter expressing viruses belonging to different families methods of characterization and applications to facilitate the study of in vitro and in vivo viral infections contrasting advantages we also seek to discuss disadvantages associated with these reporter expressing viruses. To circumvent this requirement replication competent iav expressing an easily traceable reporter protein can be used here we discuss the development and applications of recombinant replication competent iav harboring diverse fluorescent or bioluminescent reporter genes in different locations of the viral genome. Replicating competent reporter expressing viruses rcrevs are one type of artificially modified viruses that not only retain the viral genetic characteristics but also possess the new properties of the reporter genes which represent a useful tool for quantitative analysis of viral replication and tracking viral protein transport in both . Studying viral dissemination in vivo using replication competent reporter expressing iav remains a challenge because it requires that the reporter signal to be detected through tissue and skin pan et al published the generation of replication competent iav harboring gluc in the na segment using pr8 as the backbone iav gluc 72 table 5 . In summary reporter expressing replicating competent iav represent a powerful tool for the study of iav both in vitro and in vivo influenza a virus iav genome organization and virion structure