Most newly emerging infectious diseases in human populations originate from livestock or wild animals. When infected animals encounter susceptible human hosts, a novel virus may evolve that can then be transmitted from human to human. This is a low-probability event, but—as is now well known—it is an event with potentially catastrophic consequences. Land-use planners need to ensure that livestock farms, processing facilities, and markets for live animals adhere to appropriate building codes and are situated at a safe distance from human population centers. Planners also have an important role to play in ensuring that farms and other livestock facilities are managed effectively to reduce the possibility of disease transmission. Appropriate measures include regular hand washing, good water and sanitation systems, frequent checks for fever and other symptoms of human flu, prompt isolation of sick animals, and basic sick-leave compensation for farmers and farm workers.