Hypopomids are known from the continental waters of all South American countries except Chile, and are most diverse in the Amazon Basin.

Unlike the closely related Rhamphichthyidae, species of this family do not have a tubular snout, but a blunt, short one.

[2] The electric organ discharge (EOD) of these fish are multiphasic (usually biphasic), and are produced in distinct pulses.

However, species in the genus Brachyhypopomus restrict the low-frequency spectrum of their electric field close to their bodies, allowing higher frequencies to spread further; this makes it more difficult for predators to detect them.

[6] According to FishBase there are nine genera in this family,[2] but a molecular study in 2011 showed that one of these (marked with number sign# in list) should be subsumed into Hypopygus,[4] and a comprehensive molecular study from 2015 showed that two genera (marked with stars* in list) traditionally placed here belong in Rhamphichthyidae.