HBV was visualized by electron microscope in 1970. But, now direct visualization of HBV is not required for making a diagnosis of HBV infection. Like many other microbial agents, HBV infection can be assessed from the presence of various serological markers. These include several HBV DNA, HBV-related antigens and antibody. HBV DNA is the direct proof of HBV infection and this can be assessed in different clinical laboratory in the world. Hepatitis B surface antigen (HBsAg) is the most common marker of HBV infection and its presence indicate a direct proof of ongoing HBV infection. Estimation of HBsAg is cheap. In addition, anti-HBc and other HBV-related markers have their own significance and limitations for assessing clinical status of HBV-infected patients. Proper assessment and explanation of HBV-related serological markers in HBV-infected patients are vital for HBV prophylaxis and management. If these seromarkers are not appropriately understood, it would be difficult to develop patient’s conditions. A comprehensive description of different serological markers and their significance would be found in this chapter.