Hepatitis B virus is a member of the Hepadnavirus family. The virus particle, called Dane particle consists of an outer lipid envelope and an icosahedral nucleocapsid core composed of protein.
The nucleocapsid encloses the viral DNA and a DNA polymerase that has the reverse transcriptase activity which is similar to retroviruses. The outer envelope contains embedded proteins which are involved in viral binding of, and entry into, susceptible cells.
Hepatitis B virus is classified as the type species of the Orthohepadnavirus, which contains eight other species. The genus is classified as part of the Hepadnaviridae family, which contains one other genus, Avihepadnavirus.
The virus is divided into four major serotypes (adr, adw, ayr, ayw) based on antigenic epitopes present on its envelope proteins. | 
