The different components of the immune system play important roles in the outcome of hepatitis B and C. In > 90% of HBV-infected individuals, these immune responses successfully clear the virus, while 50-80% of chronically HCV-infected individuals experience viral persistence. During the last years, the mechanisms of viral persistence, e.g. viral escape mutations and T cell dysfunction, have been characterised in more detail. The exact knowledge of the mechanisms contributing to viral clearance and persistence are prerequisite to the successful development of prophylactic and therapeutic immunostrategies.