The body plan of the combtooth blennies is archetypal to all other blennioids; their blunt heads and eyes are large, with large continuous dorsal fins (which may have 3-17 spines). Their bodies are compressed, elongate and scaleless; the small, slender pelvic fins (which are absent in only two species) are situated before the enlarged pectoral fins, and the tail fin is rounded. As their name would suggest, combtooth blennies are noted for their comb-like teeth lining their jaws.
By far the largest species is the eel-like hairtail blenny at 53 centimetres in length; most other members of the family are much smaller. Combtooth blennies are active and often highly colourful, making them popular in the aquarium hobby.
Generally benthic fish, combtooth blennies spend much of their time on or near the bottom. They may inhabit the rocky crevices of reefs, burrows in sandy or muddy substrates, or even empty shells. Generally found in shallow waters, some combtooth blennies are capable of leaving the water for short periods during low tide, aided by their large pectoral fins which act as "feet". Small benthic crustaceans, mollusks and other sessile invertebrates are the primary food items for most species; others eat algae or plankton.
There is one exceptional group of combtooth blennies which deserve special mention: the so-called sabre-toothed blennies of the genera Aspidontus, Meiacanthus, Petroscirtes, Plagiotremus, and Xiphasia. These blennies have fang-like teeth with venom glands at their bases. Species of the genera Apistodontus and Plagiotremus (such as the false cleanerfish) are noted for their cunning mimickry of cleaner wrasses: by imitating the latter's colour, form and behaviour, the blennies are able to trick other fish (or even divers) into letting down their guard, long enough for the blennies to nip a quick mouthful of skin or scale.
Some combtooth blennies will form small groups, while others are solitary and territorial. They may be either diurnal or nocturnal, depending on the species. Females lay eggs in shells or under rock ledges; males guard the nest of eggs until hatching. In some species the eggs may remain in the oviduct of the female until hatched. The fry of some species undergo an ophioblennius stage, wherein the fish are pelagic (i.e., inhabiting the midwater) and have greatly enlarged pectoral fins and hooked teeth.