Hepatitis B virus is a serious public health problem worldwide and major cause of acute and chronic hepatitis, cirrhosis and hepatocellular carcinoma (HCC). It was estimated that approximately 30% of the world's population, or about 2 billion people have serological evidence of past or present HBV infection. It was reported that 15-40% of HBV infected patients would develop cirrhosis, liver failure or HCC and 500,000 to 1.2 million people die of HBV infection annually. The high resistance of HBV to inactivation and its high concentration in blood and other body fluids such as saliva, semen, vaginal secretion, breast milk and tears accounts for its high infectivity. Health care workers, haemophiliacs and other persons who have received regular transfusions of blood and blood products are at increased risk of infection. The overall aim of this book is to investigate the infectivity of saliva of HBV chronic carriers through detection of HBV antigens and their corresponding antibodies and HBV DNA.