This talk will focus on occult hepatitis B infection which largely affects individuals born in countries where hepatitis B virus infection is common. Although it is still debated whether occult hepatitis B infection is harmful to the host and linked to the development of liver cancer, it is clear that infection can spread via blood transfusion. Transmission of undiagnosed HBV infections in renal dialysis units is also a concern. While more sensitive methods have been developed to identify those with previous exposure to HBV and current active infections, better markers are needed to predict the individuals who are infectious through transfusion or transplant, and those who are most at risk of developing severe infection outcomes.