Vespertilionidae is a family of microbats, of the order Chiroptera, flying, insect-eating mammals variously described as the common, vesper, or simple nosed bats.

They are allied to the suborder Microchiroptera, the families of microbats separated from the flying foxes and fruit bats of the megabat group Megachiroptera.

The ultrasound signal is usually produced orally, and many species have large external ears to capture and reflect sound, enabling them to discriminate and extract information.

[5] Some are relatively slow-flying genera, such as Pipistrellus, that manipulate the configuration of their broader wing shape and may give a fluttery appearance as they forage and glean.

The size range of the family is 3 to 13 cm (1.2 to 5.1 in) in head and body length; this excludes the tail, which is itself quite long in many species.

[6] Most species roost in caves, although some make use of hollow trees, rocky crevices, animal burrows, or other forms of shelter.

[7] Subfamilies that were once recognized as valid, such as the Nyctophilinae, are considered dubious, as molecular evidence suggests they are paraphyletic in their arrangements.