Virology is the scientific study of viruses. It focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy. Virology is a subfield of microbiology.

The identification of the causative agent of tobacco mosaic disease (TMV) as a novel pathogen by Martinus Beijerinck (1898) is now acknowledged as being the official beginning of the field of virology as a discipline distinct from bacteriology. He realized the source was neither a bacterial nor a fungal infection, but something completely different. Beijerinck used the word ‘virus’ to describe the mysterious agent in his ‘contagium vivum fluidum’ (‘contagious living fluid’). Rosalind Franklin proposed the full structure of the tobacco mosaic virus in 1955.

Virology began when there were no methods for propagating or visualizing viruses or specific laboratory tests for viral infections. The methods for separating viral nucleic acids (RNA and DNA) and proteins, which are now the mainstay of virology, did not exist. Now there are many methods for observing the structure and functions of viruses and their component parts. Thousands of different viruses are now known about and virologists often specialize in either the viruses that infect plants, or bacteria and other microorganisms, or animals. Viruses that infect humans are now studied by medical virologists.

Virology is a broad subject covering biology, health, animal welfare, agriculture and ecology. There are many methods used for studying viruses and this article outlines the principal ones and those of historical importance.