The Hu laboratory researches Hepatitis B virus (HBV). It represents a significant human pathogen, with over 300 million people infected worldwide. Chronic HBV infection not only results in fatal liver diseases such as cirrhosis and liver failure but also dramatically increases the risk of liver cancer by over 100-fold. HBV infections present a fascinating system to study mechanisms of viral replication, virus-host interaction, and viral pathogenesis. HBV replicates a peculiar circular DNA genome via a reverse transcription pathway that is similar to, yet distinct from, that of retroviruses. The outcome of HBV infection ranges from transient, self-resolving acute hepatitis to life-long viral persistence with or without apparent liver pathology and its attendant sequelae. Viral clearance or persistence is clearly determined by the intricate interplay of a multitude of still largely undefined viral and host factors. They are focusing their studies on the virus-host interactions, at the molecular and cellular level, which are critical to HBV replication and pathogenesis.