Viruses are minute, non-living entities that copy themselves once inside the living host cells. All living organisms (animals, plants, fungi, and bacteria) have viruses that infect them. Typically viruses are made up of coat (or capsid) that protects its information molecule (RNA or DNA); these information molecules contain the blue prints for making more virus. The viruses are highly diverse in their shape, size, genetic information, and infectivity. Viruses are all around us, on an average a human body encounters billion virus particles every day. Our intestinal, respiratory, and urogenital tract are reservoirs for many different kinds of viruses, it is astonishing that with such constant exposure, there is little or no impact of these organisms in human health. The host defense mechanism is quite strong to remove all these in normal condition, while they cause many nasty diseases only when the person is immune-compromised . Although viruses have a limited host range but sometimes they may jump the species barrier and causes fatal disease, recent spread of swine influenza is an ideal example of such kind of spread.

The epidemic viruses, such as influenza and severe acute respiratory syndrome (SARS), cause diseases that rapidly spread to a large human population within no time, and seem to attract more scientific and public attention than do endemic viruses, which are continually present in a particular population.

Virology as a discipline is merely 100 years old and the way it expanded in this small period of time is rampant. To group the new emerging viruses in a specific group by specifying certain parameters was initiated in 1966 when international committee on the taxonomy of viruses (ICTV) was formed with the aim to classify the viruses. The ICTV has adopted a norm for the description of the viruses. Name for genera, subfamilies, families, and orders must all be a single word, ending with the suffixes -virus , -virinae , -viridae , and -virales respectively. In written usage, the name should be capitalized and italicized.