Classical swine fever virus (CSFV) is a small enveloped virus and a member of the genus pestivirus belonging to the family Flaviviridae. Its genome is a single stranded positive sense RNA. A 5’noncoding region that fonctions as an internal ribosome entry site (Ires) and a 3’ noncoding region nonpolyadenylated flank an open reading frame encoding a single viral polyprotein. With the exception of one nonvirion protein, viral structural proteins are located in the N-terminal part of the polyprotein. Nonstructural or RNA replicase components are located in remainder of the polyprotein. Animal infection with CSFV gives variable symptomatology depending on the virulence of the strain, host factors as age, the physiological state and the stage of fœtal development. Classical swine fever consists in a highly contagious septicaemia which is fatal under acute form. The laboratory diagnosis could be direct by virus isolation and/or indirect by antibodies screening. Epidemiological survey of CSFV during an outbreak is done by sequencing of RT-PCR products. Even if vaccination is forbidden in European Community some groups still work for the production of new vaccine against CSFV.