The International Committee on Taxonomy of Viruses (ICTV) held meetings in Madrid in September 1975, reviewing the classification and nomenclature of viruses. The results include updates to the rules of viral nomenclature, the composition of the new Executive Committee, and a list of officially agreed names. The ICTV has established rules for viral nomenclature, including the use of Latinized names for genera and families, and the acceptance of sigla (abbreviated names) if they are meaningful and recommended by international groups. The rules also state that names should be international, universally applicable, and not based on personal names. The new Executive Committee includes members such as R. E. F. Matthews as President and H. G. Pereira as Vice-President. The meeting also approved new names for plant virus groups that had been proposed in 1970. Viruses primarily of interest to vertebrate virologists have been more thoroughly studied due to their medical and veterinary significance and the availability of cell culture systems. These viruses are classified into families and genera, with some still monogenetic. Plant virology is less advanced due to fewer workers and the lack of a well-developed cell culture system. The Plant Virus Subcommittee approved new names for several viral groups, including Bromovirus, Cucumovirus, and Nepovirus. Invertebrate virology has seen growing evidence of viruses in all invertebrate groups, including some that may belong to families previously characterized in vertebrates or plants. Bacterial virology has revealed a wide variety of bacterial viruses, with some proposed families such as Myoviridae, Styloviridae, and Corticoviridae. The meeting also discussed the need for further classification and naming of bacterial viruses. The ICTV aims to ensure that information on viral taxonomy is available to virologists worldwide, with the publication of a separate volume of "Intervirology" detailing the results of the meetings.The International Committee on Taxonomy of Viruses (ICTV) held meetings in Madrid in September 1975, reviewing the classification and nomenclature of viruses. The results include updates to the rules of viral nomenclature, the composition of the new Executive Committee, and a list of officially agreed names. The ICTV has established rules for viral nomenclature, including the use of Latinized names for genera and families, and the acceptance of sigla (abbreviated names) if they are meaningful and recommended by international groups. The rules also state that names should be international, universally applicable, and not based on personal names. The new Executive Committee includes members such as R. E. F. Matthews as President and H. G. Pereira as Vice-President. The meeting also approved new names for plant virus groups that had been proposed in 1970. Viruses primarily of interest to vertebrate virologists have been more thoroughly studied due to their medical and veterinary significance and the availability of cell culture systems. These viruses are classified into families and genera, with some still monogenetic. Plant virology is less advanced due to fewer workers and the lack of a well-developed cell culture system. The Plant Virus Subcommittee approved new names for several viral groups, including Bromovirus, Cucumovirus, and Nepovirus. Invertebrate virology has seen growing evidence of viruses in all invertebrate groups, including some that may belong to families previously characterized in vertebrates or plants. Bacterial virology has revealed a wide variety of bacterial viruses, with some proposed families such as Myoviridae, Styloviridae, and Corticoviridae. The meeting also discussed the need for further classification and naming of bacterial viruses. The ICTV aims to ensure that information on viral taxonomy is available to virologists worldwide, with the publication of a separate volume of "Intervirology" detailing the results of the meetings.