This review is written for the series celebrating the 40th year since the first issue of Avian Pathology. The aim of the authors was to cover the developments in Newcastle disease (ND) research over the last 40 years that they considered significant. During those 40 years there have been several panzootics of this serious disease in poultry and for the last 30 years there has been a continuing panzootic in domestic pigeons, which has spread to wild birds and poultry. The 40-year period began with worldwide outbreaks of severe ND, which served as an important impetus for ND research work. Although early work was concerned with controlling the disease, specifically by improving and developing new vaccines and vaccine regimens, even prior to the 1970s ND virus was seen as a useful laboratory virus for replication and virulence studies. This review covers the historical developments in the following areas: understanding the molecular basis of virulence; epidemiology and relatedness of different ND strains, both antigenically and genetically; the emergence of virulent strains and their relationship with viruses of low virulence; sequencing and understanding the viral genome and genes; the development of rapid molecular-based diagnostic tests; and the phylogeny and molecular taxonomy of ND virus. The authors suggest areas in which future research could or should be undertaken.