Inuenza A virus (IAV) belongs to the family Orthomyxoviridae, and the genome is composed of eight singlestranded, negative-sense RNA segments. IAV can infect a wide range of host species such as birds (wild and domestic), bats, and mammals (including humans, pigs, horses, dogs, and cats) [1]. The epidemiology and ecology of IAVs are complicated due to the multihost and segmented genome. In swine, IAVs are one of the major pathogens that cause acute respiratory disease and result in substantial economic burden to swine producers. In addition to swine IAVs, human and avian IAVs can also infect swine. Swine have been thought to serve as an intermediate “mixing vessel” for the generation of diversied and novel inuenza viruses [2]. There have been numerous reports of zoonotic human infections with swine IAVs and reverse zoonotic swine infections with human IAVs [3-7]. Therefore, swine hosts and swine IAVs are important components of the “one health” concept. Detection and characterization of swine IAVs are not only necessary for surveillance, control, and prevention of swine inuenza but also critical for public health purposes. In this chapter, swine IAV classication, genome organization, epidemiology, clinical features and pathogenesis, and diagnosis are described.