The Chinese character “Home” is composed of two parts: the upper part as a roof of a house and the lower part as a pig. This depicts the close relationship and frequent interactions between the swine and the humans and also highlights the important role a pig played in an agricultural society. To understand the swine influenza and the genesis and development of the 2009 pandemic H1N1, our learning objectives are focused on, the role of the domestic pigs in influenza ecology, the history of swine influenza, the emergence and development of the pandemic 2009 H1N1 virus. Ecologically, pigs were considered as one of the major mammalian hosts of the influenza A viruses and the hypothetic mixing vessels; which can facilitate the genesis of novel reassortant variants with genes of the avian, swine, and human origins. They can also act as intermediate hosts for the mammalian adaptation of avian viruses, which may later acquire the ability to transmit to humans. Biologically, pigs possess both the alpha 2,3 and alpha 2,6 sialic acid receptors for avian and human influenza viruses respectively, and are susceptible to both viruses. The ecological overlaps between the swine habitats with those of the birds, and the humans, promote the chance for virus interspecies transmissions. Although two-way; transmissions of influenza viruses between humans and swine were frequently observed, stable lineage establishment of the wholly human influenza viruses was not common in pigs. However, the human seasonal influenza virus did contribute some gene segments to the currently prevailing swine influenza virus lineages. Historically, only three influenza viruses have been successfully established in the domestic pigs all over the world. These are the Classical swine influenza H1N1 lineage, demonstrated in blue, the Eurasian avian-like H1N1 lineage, colored in green, and the North American triple reassortant swine influenza virus lineage, in orange. The Classical swine lineage has been established in pigs for more than 90 years, and the North American triple reassortant lineage was actually a derivation from this Classical swine lineage, which occurred in around year 1998. In Europe, an avian-like H1N1 virus first emerged in year 1979, and quickly replaced the once predominant Classical swine influenza virus. In the mid-1980’s, this H1N1 virus reassorted with a human seasonal H3N2 virus to generate a reassortant virus with the Port Chalmers-like H3N2 surface genes. In Asia, both the European avian-like H1N1 virus and its reassorted H3N2 variant, were introduced to the swine population in China and Thailand in around year 1999 and sporadically caused some human infections. The North American triple reassortant H1N2 virus was also introduced to Asia shortly after the occurrence of the European avian-like H1N1 virus in this region. This virus was repeatedly introduced from North America to China and Korea and was regularly isolated in both countries. The co-circulation of the Classical swine lineage together with Eurasian avian-like H1N1 and the North American triple reassortant viruses finally generated the swine-origin pandemic H1N1 virus in year 2009. This highly reassorted virus obtained its NA and M gene segments from the Eurasian avian-like virus lineage and the other genes from the North American triple reassortant viruses. Phylogenetically, its HA, NP and NS genes were derived from the Classical swine lineages, PB1 gene from the human seasonal H3N2 lineage, and the PB2 and PA genes from the avian origins. Before the introduction and emergence of the European avian-like and the North American triple-reassortant viruses into China, only the Classical Swine influenza virus and the human-like influenza viruses were co-circulating in the local pig population. The first wave of swine influenza virus reassortment started in the late 1990s, when international trading of live pigs from Europe and from North America became very popular in this developing country. The second wave of the genotypic expansion of the swine influenza viruses in China began in year 2009, right after the introduction of the pandemic H1N1 virus into the pigs. The repeated introduction of this virus from the human resource and extensive reassortment of this virus with enzootic swine viruses in the field has produced a wide range of novel reassortants. Some of them have been proved to be infectious to human beings. In North America, a novel triple reassortant H3N2 variant, which acquired M gene segment from the pandemic 2009 virus, has caused more than 300 human infection cases since year 2011. Therefore, the introduction of the pandemic 2009 H1N1 virus into the pig population has profoundly changed the landscape of swine influenza. gene pool and raised public concerns that further reassortment may result in the generation of novel viruses with the potential to infect humans. Monitoring the evolution and ecology of the influenza virus is an essential task for human well being. This is especially the case in Asia where the largest population of pigs in the world interacts with the largest human population.