Hybridoma technology for production of monoclonal antibodies is one of the most important advancements in the field of immunology. Monoclonal antibodies (Mabs) have been extensively used for the diagnosis of wide spectrum of viral and other infectious diseases, analysis of important immunogenic regions (epitopes) for better control and prevention of diseases. The Mabs can be used with advantage of high sensitivity and specificity in enzyme linked immunosorbent assay (ELISA), neutralization and other serological tests. Use of Mabs in ELISA provides useful aid to the epidemiologist in the differentiation of virus strains and tracing the source of outbreak with greater certainty. The Mabs are also used, profitably to differentiate the rinderpest from peste des petits ruminant (PPR) virus, different strains of bovine viral diarrhoea, foot-and- mouth disease virus strains, study of antigenic variation in equine influenza, understanding the immunobiology and development of antigenic variants of equine infectious anaemia (EIA) virus in persistent infection; differentiation between EHV-I and EHV-IV and between North and South American strains of eastern equine encephalomyelitis and other closely related virus strains/isolates. With the advent of fluorescence-activated cell sorter (FACS), cell surface markers can be tagged with monoclonal antibodies for their identification and quick screening of population of particular cell type or biomarker on the cell surface.