The henipavirus genus has two members – the Hendra virus (HeV) and the Nipah virus (NiV). HeV and NiV, identified in the 1990s as a paramyxovirus, cause fatalities in humans and animals. They are now classified as biosafety level 4 pathogens. HeV caused fatal respiratory infection in horses and humans in Australia in 1994, in which 2 persons died. The first-known, largest NiV outbreak occurred on theMalay Peninsula in 1998, in pigs and humans. The human fatality rate was 40%, killing 105. To cope, the Malaysian government culled over 1 million pigs at huge economic loss. The natural virus reservoir, the fruit bat (Pteropus), inhabits areas from Australia, through South Asia to Africa. InMalaysia, NiV to humans was through pigs, and the reemergence has never observed after that. However, sporadic outbreaks of NiV are continuously occurring in Bangladesh and India, in some of which epidemics human mortality exceeds 75%. The transmission is directly from fruit bats to humans, and even human-to-human transmissions are found. To prevent the outbreaks, it is important to have an intense monitoring for these diseases, to accumulate basic knowledge about the viruses and the diseases, and to develop effective vaccines.