Birch mice are small jumping rodents that resemble mice with long, tufted tails and very long hind legs, allowing for remarkable leaps. They are the only extant members of the family Sminthidae. They were formerly classified as part of the subfamily Sicistinae in the family Dipodidae alongside the jerboas and jumping mice. However, phylogenetic evidence supports all three of these belonging to distinct families, thus leaving only the jerboas in Dipodidae and promoting Sicistinae to its own family.