This Virology textbook is intended for Licence 2 students in Medical Biology, Medicine, Pharmacy, Odontostomatology and Biology. The first part deals with the introduction to virology, definition of viruses, history, general characters, specificity of viruses, their dependence on host cell metabolism, structure of viruses (genome, capsid, lipid membrane, envelope, matrix, anti-receptors, naked viruses and enveloped viruses), helically symmetrical viruses, icosahedral symmetrical viruses and viruses with complex architecture. Viral taxonomy, the concept of viral species, the specificity of viral taxonomy, the collection and conservation of viruses, the development cycle according to the nature of the viral genome, the special case of plant viruses, etc. Special virology which deals with the new viruses and the diseases they cause in humans in detail. These include HIV, Poliovirus, SARS Cov 2, Hepatitis B Virus, Lassa Virus, Ebola Virus, Marburg Virus, Influenza Virus and Measles Virus. The final section covers diagnostic methods for viral infectious diseases.