The species included in this family are mainly small (not larger than 1 cm, but most species are less than 3 mm) and brown or blackish. Their body shape is generally elongate and dorsoventrally flattened, the eyes are globose and relatively large. The beetles usually live near or in water, but are not adapted to free swimming and instead walk under water. They share with the Hydrophilidae the peculiar mode of breathing by "scooping" air with their antennae. The beetles come close to the water surface and use the beating movement of their antennae to transport air from the surface to the ventral side of their body. The air is trapped in fine hair that is present both on the antennae and on the ventral side of the body. Because the antennae are used for breathing, the sensory function has been transferred almost completely to the palps of the maxillae, and therefore in most species these palps are also much longer than the antennae (and are easily mistaken for them!).

The eggs are deposited singly on water plants or stones, sometimes protected by a thin web of silk threads secreted by the female. Imagines and larvae often share the same habitat and both feed on algae, in some species, however, the larvae live on land. Pupation always occurs on land and only the imago returns into the water. Species of the genus Ochthebius build a cocoon of mud around their pupa.