The oral cavity is a home to rich microbial flora and different species have been identified. The focus has traditionally been on bacteria and fungi when discussing microbiological aspects of oral disease. Viruses are probably more involved in diseases associated with the oral cavity than has been previously thought. Viruses are by nature more difficult to detect, at least with traditional methods such as in vitro cultivation. The field of virology has advanced greatly over the past two decades mainly because of the introduction of sophisticated molecular tools. An important point to keep in mind is that the likelihood of healthcare-associated infections, particularly in dentistry, of being detected, reported, documented and published is small. This book includes a comprehensive review of the viruses, viral classification, structure, clinical features, diagnosis, prevention and the oral manifestations of viral diseases. This can be very helpful for the early diagnosis and treatment of viral diseases by clinicians and oral diagnostic.