Hepadnaviruses are a family of viruses which can cause liver infections in humans and animals. There are two recognized genera:

The name of the family comes from : hepa(for HEPAtic)-DNA-virus.

Hepadnaviruses have very small genomes of partially double-stranded, partially single stranded circular DNA. The genome consists of two uneven strands of DNA. One has a negative-sense orientation, and the other, shorter, strand has a positive-sense orientation.

As it is a group 7 virus, replication involves an RNA intermediate. Three main open reading frames are encoded (ORFs) and the virus has four known genes which encode the core protein, the virus polymerase, surface antigens (preS1, preS2, and S) and the X protein. The X protein is thought to be non-structural; however, its function and significance are poorly understood.

Hepadnaviruses replicate through an RNA intermediate (which they transcribe back into cDNA using reverse transcriptase). The reverse transcriptase becomes covalently linked to a short 3- or 4-nucleotide primer. Most hepadnaviruses will only replicate in specific hosts, and this makes experiments using in vitro methods very difficult.