Control strategy of hepatitis B virus (HBV) infections and successful vaccination against them require an understanding of the nature and variability of the epidemic behavior among genotypes, subtypes and mutated forms of the hepatitis viruses in a particular community. India is vast country having about 40 million people are chronically infected with HBV. However, limited data is available regarding genotype distribution and the nature of mutant strain circulating in India. It is now well established that genotype distribution can vary within a country depending upon the ethnicity of the population as well as the history of human migration. The geographical location of Eastern India is distinct in comparison to other parts of the India. It borders with China, Tibet, Myanmar and Bangladesh and had a past history of population migration through the North East corridor. Therefore, it is very important to know the prevalence and HBV genotype distribution, mode of transmission and subsequent clinical outcome in this region. This book will provide a comprehensive picture about the origin and natural variability of HBV genotype in Eastern India and their association with clinical outcome.