The symptom modulating, single-stranded DNA satellites (known as DNA ) associated with begomoviruses (family Geminiviridae) have proven to be widespread and important components of a large number of plant diseases across the Old World. Since they were first identified in 2000, over 260 full-length sequences (~1360 nucleotides) have been deposited with databases and this number increases daily. This has highlighted the need for a standardised, concise and unambiguous nomenclature for these components, as well as a meaningful and robust classification system. Pairwise comparisons of all available full-length DNA sequences indicates that the minimum numbers of pairs occur at a sequence identity of 78%, which we propose as the species demarcation threshold for distinct DNA . This threshold value divides the presently known DNA sequences into a tractable 51 distinct satellite species. In addition we propose a naming convention for the satellites that is based upon the system already in use for geminiviruses. This maintains, whenever possible, the association with the helper begomovirus, the disease symptoms and the host plant and provides a logical and consistent system for referring to already recognised and newly identified satellites.Estación Experimental "La Mayora", Consejo Superior de Investigaciones Científicas, 29750 Algarrobo-Costa, Málaga, Spain. National Institute for Biotechnology and Genetic Engineering, Jhang Road, P.O. Box 577, Faisalabad, Pakistan. Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA. John Innes Centre, Colney Lane, Norwich, NR4 7UH, UK. Departamento de Fitopatologia, Universidade Federal de Viçosa, Viçosa, MG 36570-000, Brazil. Institute of Biotechnology, Zhejiang University, Hangzhou 310029, China. ILTAB/Danforth Plant Science Centre, 975 N. Warson Rd., St. Louis, MO63132, USA.Peer reviewed