Hepatitis B virus (HBV) is a major global health problem, infecting over 250 million people worldwide. It is transmitted through bodily fluids and can result in both acute and chronic infections. Chronically infected individuals are at high risk of developing liver cancer. HBV is an enveloped virus that contains DNA and replicates through an RNA intermediate using its reverse transcriptase. It has a strict tropism for liver cells. Diagnosis involves detecting various viral proteins and antibodies through serological testing. Prevention includes vaccination with a subunit vaccine based on the hepatitis B surface antigen.