Studying iav in vitro or in vivo requires the use of laborious secondary methodologies to identify virus infected cells 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 these viruses have been employed for in vitro and in vivo . 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. 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 living cells and animals. Stable incorporation of foreign genes in replication competent reporter expressing iav allows for effective tracking of viral infection in vitro and in vivo enabling a robust quantitative readout this readout can be used with high throughput screenings hts and to assess viral infection in tissue. Replication competent influenza a viruses expressing reporter genes michael breen aitor nogales steven f baker luis martinez sobrido affiliations michael breen department of microbiology and immunology university of rochester school of medicine and dentistry 601 elmwood avenue rochester ny 14642 usa aitor nogales department of microbiology and immunology university of rochester