Viruses are infectious agents that consist of genetic material (either DNA or RNA) surrounded by a protein coat (called a capsid), and some viruses also have an outer envelope. They are not considered living organisms, as they cannot reproduce on their own and require a host cell to replicate. Virology plays a crucial role in understanding the nature of viral diseases and the development of vaccines and antiviral therapies. Through research in virology, scientists have discovered how viruses enter cells, replicate, and evade the immune system, leading to the development of antiviral drugs that can target these processes. Furthermore, virology helps us to understand how viruses are transmitted between hosts, which is crucial for developing public health strategies to control the spread of viral diseases. Understanding the epidemiology of viral diseases is also important for outbreak investigations and disease surveillance.