Favipiravir (T-705) is a novel antiviral drug that selectively inhibits the RNA-dependent RNA polymerase (RdRP) of influenza viruses. It is converted to its active form, favipiravir-ribofuranosyl-5′-triphosphate (RTP), by cellular enzymes. The antiviral effect is reduced by the addition of purine nucleic acids, indicating that the viral RdRP misrecognizes RTP as a purine nucleotide. Favipiravir is effective against a broad range of influenza viruses, including pandemic and highly pathogenic strains, and shows synergy with oseltamivir. Phase III clinical trials in Japan and two Phase II studies in the United States have been completed. In addition to its activity against influenza, favipiravir blocks the replication of several other RNA viruses, including arenaviruses, bunyaviruses, flaviviruses, enteroviruses, alphaviruses, paramyxoviruses, and noroviruses. Its unique mechanism of action and broad antiviral spectrum make it a promising candidate for treating influenza and other RNA viral diseases.Favipiravir (T-705) is a novel antiviral drug that selectively inhibits the RNA-dependent RNA polymerase (RdRP) of influenza viruses. It is converted to its active form, favipiravir-ribofuranosyl-5′-triphosphate (RTP), by cellular enzymes. The antiviral effect is reduced by the addition of purine nucleic acids, indicating that the viral RdRP misrecognizes RTP as a purine nucleotide. Favipiravir is effective against a broad range of influenza viruses, including pandemic and highly pathogenic strains, and shows synergy with oseltamivir. Phase III clinical trials in Japan and two Phase II studies in the United States have been completed. In addition to its activity against influenza, favipiravir blocks the replication of several other RNA viruses, including arenaviruses, bunyaviruses, flaviviruses, enteroviruses, alphaviruses, paramyxoviruses, and noroviruses. Its unique mechanism of action and broad antiviral spectrum make it a promising candidate for treating influenza and other RNA viral diseases.