The Baltimore classification of viruses is based on the mechanism of mRNA production. This classification places viruses into seven groups:

dsDNA viruses (e.g. Adenoviruses, Herpesviruses, Poxviruses)

ssDNA viruses (+)sense DNA (e.g. Parvoviruses)

dsRNA viruses (e.g. Reoviruses)

(+)ssRNA viruses (+)sense RNA (e.g. Picornaviruses, Togaviruses)

(-)ssRNA viruses (-)sense RNA (e.g. Orthomyxoviruses, Rhabdoviruses)

ssRNA-RT viruses (+)sense RNA with DNA intermediate in life-cycle (e.g. Retroviruses)

dsDNA-RT viruses (e.g. Hepadnaviruses)