The Miniopteridae were previously treated as a subfamily of the Vespertilionidae. However, this family differs in a number of morphological, embryological, immunological, and genetic ways from the Vespertilionidae (Hoofer and van den Bussche 2003, Eick et al. 2005). For example, the best-known character of this group is the uniquely elongated second phalanx of the third digit, which allows the wing to ‘bend’ back onto itself, hence the alternative name ‘bent-wing bats’. The second phalanx is more than three times the length of the first phalanx; in vespertilionid bats, by contrast, it is usually not more than twice the length of the preceding phalanx. The lengthening of this digit (Figure 246a) gives the wing its long and narrow shape, allowing it to fly swiftly and efficiently in open areas. This family typically also has a raised braincase (Figure 246b). Molecular studies have revealed that this group does indeed deserve familial status, having diverged from their closest relatives, the Vespertilionidae, about 38–49 million years ago (Miller-Butterworth et al. 2007). The Molossidae had diverged from these two lineages about 10 million years earlier.

This family is represented by the single genus Miniopterus. Of the six currently recognised African species, four have been recorded in southern Africa. Although members of this genus are readily identifiable in the field owing to the greatly elongated third finger, distinguishing between the species is often difficult. Recent molecular evidence reveals that Miniopterus is comprised of several overlooked cryptic species in Africa.

The five southern African species differ in body size, but this is only absolute for skull length, although there is overlap even in this measurement between any two taxa. They emit low duty-cycle, frequency-modulated (LD-FM) echolocation calls. Analysis of cytochrome-b sequences indicate that the largest and smallest of the three South African species, M. inflatus and M. fraterculus, are each other's closest relatives, while M. natalensis (which overlaps in size with both these species) is more distantly related (Miller-Butterworth et al. 2005). A more comprehensive phylogeny that includes all five southern African species shows that M. fraterculus and M. minor are sister taxa; these two in turn are sister to M. inflatus, with the newly described M. mossambicus being basal to all three of these species. The fifth species, M. natalensis, is more distantly related to the other four miniopterids (Monadjem et al. 2013a, 2019).