Hendra virus (HeV) is closely related to Nipah virus (NiV) and both are the founding members of the genus Henipavirus, family Paramyxoviridae. HeV emerged in the 1990s as the cause of zoonotic outbreaks. In 1994, HeV caused severe respiratory disease and the death of 13 horses and a horse trainer in Brisbane, Australia. HeV has caused the death of four of seven infected people in Australia. Fruit bats (flying foxes) in the genus Pteropus are natural hosts of both viruses. HeV infection of horses presents with a wide range of clinical signs that can include sudden death, high fevers, severe respiratory difficulty and ataxia. Some horses display neurological signs while others have presented with colic-like signs. HeV infection of horses is not uniformly fatal, nor does it appear to be highly contagious among horses, with close contact necessary for its spread. Infected horses on pastures have rarely transmitted the virus to other horses. Transmission appears to occur more readily in closed environments such as stables and veterinary clinics. HeV can infect companion animals but does not seem to play a role in the epidemiology of the disease. Infection of humans is from animal contact, usually from an amplifier host rather than directly from the reservoir host: HeV from horses. HeV is a dangerous human pathogen. All laboratory manipulations with live cultures or potentially infected/contaminated material must be performed at an appropriate biosafety and containment level.