Clausiliidae are a family of pulmonate landsnails (Stylommatophora) with sinistral, turreted shells with interior wall-folds, which are developed as a closing apparatus. This so-called clausilial apparatus = CA, which is in the two lowermost whorls of the adult shell, comprises the clausilium, a plate attached to the columella by a flexible stalk, and folds on the inner and outer wall of the shell (parietal and columellar lamellae, palatal plicae). The clausilium closes the lumen of the shell, when the animal retreats, and is pushed out of the way, when the animal extends to be active.
Clausiliidae are mainly distributed in Europe, East Asia and South America. The range comprises the zoogeographic regions of western Palaearctic (one group extending to eastern Ethiopian), Oriental without peninsular India and part of eastern Palaearctic, and northern and western Neotropical.
Fossil Clausiliidae are known since the Upper Cretaceous and traced through the whole Cenozoic.
Clausiliidae are a speciose family. The currently recognized taxa numbers are as follows: 6 extant and 2 extinct subfamilies, with about 1300 extant and 160 extinct species.