Occult Hepatitis B Virus (HBV) infection (OBI) is defined as the long-lasting persistence of HBV genomes in the hepatocytes of individuals testing negative for HBV surface antigen (HBsAg) by currently available assays and usually for serum HBV DNA. OBI is considered as the possible phase in the natural history of chronic HBV infection that the host's immune surveillance and epigenetic mechanisms are likely involved. Clinical impact of OB is that it can be transmitted (i.e., through blood transfusion, by liver organ transplantation, hemodialysis and parturition) causing classic forms of hepatitis B in newly infected individuals. The development of an immunosuppressive status may induce OBI reactivation and development of acute and often severe hepatitis. OBI can favor the progression of liver fibrosis. Also OBI infection has been hypothesized to be a significant risk factor contributing to the progression of chronic liver diseases (CLD) with increased risk for hepatocellular carcinoma (HCC) which may lead to an increased progression of liver diseases. Although OBI is considered a phase in the natural history of HBV, the molecular mechanisms leading to its occurrence and its contribution to HCC development are yet poorly understood. In this review, it is aimed to examine clinical importance, epidemiological aspects and laboratory diagnosis of OBI in recent literature.