Tests to detect the presence and activity of hepatitis B virus (HBV) are the cornerstones of diagnosis and management. Assays that detect or measure serum levels of HB surface antigen, HB surface antibody, and HB core antibody are used to identify patients with exposure to HBV, whereas other tests provide information on the level of virus replication, the presence of specific variants, and presence of virus reservoirs. Newer diagnostic tests, used only in research settings so far, aim to quantify levels of intrahepatic HBV replication.