Technical Abstract: Newcastle disease (ND) is one of the most important diseases of poultry and other avian species. The nature and magnitude of this worldwide problem varies among countries from those with recurrent outbreaks of ND characterized by high mortality to those where only mild respiratory infections or in some cases no evident disease occurs. Recent ND outbreaks in Australia, Mexico, and the United States are examples of cases where low virulence virus mutated to the virulent form, inadequacies in the vaccination program, and the probable movement of smuggled birds, respectively were initiating factors in establishing those outbreaks. Outbreaks of virulent ND will continue to occur in poultry and those outbreaks will result in embargoes on shipments of poultry and poultry products. To minimize occurrence of ND outbreaks, strong biosecurity programs are needed to reduce virus transmission, appropriate vaccination programs should be developed to prevent disease, and surveillance of all poultry flocks and other bird populations to detect and recover any circulating ND virus isolates must be continuous. To accomplish ND control within any country there will have to be good communication and strong cooperation among all parties involved ' the production companies and their technical service teams, the diagnosticians, the regulatory agencies, and the research groups that support development of improved techniques for testing and appropriate control methods. Complete transparency of a comprehensive ND control and surveillance program is necessary to limit any embargoes following an outbreak.