Glirids are small to medium sized rodents, up to about 190 mm in head-body length. They resemble squirrels or chipmunks, with compact bodies and bushy tails (except members of the genera Selevinia and Myomimus, which have sparsely-furred tails). The limbs are relatively short; the feet are broad; and the toes are tipped with short, curved claws. Glirids have four functional digits on their forefeet and five on their hindfeet. Their bodies are covered with thick, soft fur. Some species have distinctive black facial markings. Most are good climbers, and arboreal species have well-developed toe pads.
Members of this family are myomorphous, but they differ somewhat from the typical myomorph arrangement of the masseter. Their skulls have an enlarged infraorbital foramen through which passes a slip of the medial masseter, as in other myomorphs, but the zygomatic plate is not as strongly developed as in most other members of the group. Nerves and blood vessels pass through this foramen as well as muscle; glirids lack the separate infraorbital foramen for the passage of nerves and blood vessels that is found in dipodids. The jugal of glirids is horizontal and does not meet the lacrimal. The mandibles are unusual in that the angular process is bent outwards, and in some genera it is perforated. Glirids are sciurognathus.
The dental formula of glirids is 1/1, 0/0, 0-1/0-1, 3/3 = 16 or 20. The incisors are sharply pointed. Cheekteeth are brachydont, and their occlusal surfaces are made up of a series of cusps and basins or parallel enamel ridges. Selevinia (which is sometimes placed in its own family) has very small teeth that scarcely erupt from the gums. These have a very simple occlusal pattern.
Other Physical Features: endothermic ; heterothermic ; homoiothermic; bilateral symmetry