Infection with peste des petits ruminants (PPR) is characterized by clinical presentation and profound immunosuppression which provide opportunity to secondary infections and enhanced disease impact on animal health. While our understandings are limited on the mechanisms of disease development in susceptible animals, knowledge on viral pathogenesis is mainly derived from related viruses such as rinderpest virus, measles virus, and canine distemper virus. In this chapter, four essential components of viral pathogenesis are critically discussed including aetiology, mechanisms of disease development (pathogenesis), structural alterations of cells morphology, and consequences of these changes manifested by clinical signs.