This article reviews virus taxonomy as of 1997, published in the Journal of General Virology. The International Committee on Taxonomy of Viruses (ICTV) has organized virus classification into hierarchical taxa: Species, Genus, Family, and Order. As of 1997, viruses are classified into 184 genera, with 161 assigned to 54 families. Two Orders exist: Mononegavirales (negative-strand RNA viruses) and Nidovirales (coronavirus-like viruses). The authors explain ICTV's four guiding principles—stability, utility, acceptability, and flexibility—and describe the organizational structure involving subcommittees and study groups of approximately 470 virologists worldwide. The International Code of Nomenclature provides rules for naming taxa. The paper discusses species definitions using a polythetic approach and examines the relationship between virus classification and phylogeny. While gene sequence comparisons have enhanced understanding of virus relationships, phylogenetic trees based on single genes (like RNA-dependent RNA polymerase) sometimes conflict with traditional classifications, particularly for RNA viruses that may have evolved through recombination and modular genome acquisition. Large DNA viruses like herpesviruses show evidence of co-evolution with hosts, supporting current taxonomies.

Key findings

• At least 184 virus genera are currently recognized and organized into 54 families and 2 orders based on genome type and biological characteristics
• ICTV operates through a democratic structure of approximately 470 virologists organized in subcommittees and study groups that propose and ratify taxonomic changes
• Virus taxonomy follows four core principles: stability of names and relationships, utility for practicing virologists, acceptability to the community, and flexibility to accommodate new discoveries
• Phylogenetic relationships deduced from single genes often conflict with traditional virus classifications, especially for RNA viruses that evolve through recombination and modular genome rearrangement
• Species classification uses a polythetic approach considering multiple biological, biochemical, and genetic characters rather than single defining features