The Retroviridae are a family of viruses that reverse transcribe their RNA genome and integrate the resulting double-stranded DNA copy into the genome of the host cell. Retroviruses are well-documented pathogens that have been associated with a variety of diseases. The International Committee on Taxonomy of Viruses (ICTV) currently lists 65 species of retroviruses. As required by the ICTV, we have converted the species nomenclature to a binomial format comprised of the genus and a freeform epithet. Assigning binomial species names to classify new retroviruses will be facilitated when following the epithet rules described herein.