AbstractThis chapter discusses the history and importance, epizootiology, infectious agent (classification, virion structure and genome organization), viral proteins (nucleocapsid protein, P gene and its encoded proteins, viral accessory proteins and their interactions with the host, matrix protein and L protein), viral glycoproteins (fusion protein and attachment protein), antigenic analysis, transcription and replication, pathogenesis, clinical signs, pathology, immunity (innate immunity and adaptive immunity), diagnosis, and the prophylaxis and control of Bovine parainfluenza virus 3.