Two names (Clethrionomys and Myodes) are used interchangeably for red-backed voles, which is contrary to one of the fundamental principles of zoological nomenclature, that each taxon has a single and unique valid name. Fixation of Mus lemmus Linnaeus, 1758, as the type of Myodes Pallas, 1811, meets the requirements stipulated in the Article 69.1.1 of the 4th edition of the International Code of Zoological Nomenclature, and is therefore valid. Hence, the genus group name Myodes is a junior synonym of Lemmus Link, 1795, and is not available for red-backed voles. The oldest valid name for red-backed voles is Clethrionomys Tilesius, 1850, with the type species (Mus rutilus Pallas, 1779) subsequently designated by Palmer (1928).