The study of viruses raises pressing conceptual and philosophical questions about their nature, their classification, and their place in the biological world. A major set of problems concerns the individuality and diachronic identity of a virus: what is the virus, the viral particle (virion) or the entire viral cycle? The correct identification of the virus has significant ontological consequences, also related to the place and time when biological entities begin and end. DOI: 10.13140/RG.2.2.35874.66241.