FeLV is classied in the genus Gammaretrovirus, subfamily Orthoretrovirinae, family Retroviridae, which includes another subfamily Spumaretrovirinae. Members of the family Retroviridae are characterized by their unique ability to transcribe their RNA into DNA upon entry into host cell and integrate their DNA (provirus) into host chromosomal DNA as an alternative means of propagation and also a potential source of oncogenic development. Taxonomically, the subfamily Orthoretrovirinae is made up of six genera (Alpharetrovirus,

Betaretrovirus, Deltaretrovirus, Epsilonretrovirus, Gammaretrovirus, and Lentivirus), while the subfamily Spumaretrovirinae is currently composed of a single genus (Spumavirus).