The majority of species are elongate, rather parallel-sided and slender with the upper surface either glabrous, finely pubescent or with broad setae which resemble narrow scales. In general the Rhizophaginae are convex, or at the very least weakly so, while many of the Monotominae are much more flattened. The North American species Pycnotomina cavicolle (Horn, 1879) is atypically broadly oval in outline while species of Thione Sharp, 1899 are very elongate with the head, and especially the temples, abnormally long. 1.5-6.0mm. The head is often large in proportion to the pronotum and usually produced forward in front of the eyes. The mandibles and palps, while well-developed, are generally not visible from above. Antennae 10-segmented with a 2-segmented club; the 10th and 11th segments are fused and so the club often appears to be a single segment, in many Monotominae the antennae are gradually thickened towards the apex. This 10-segmented arrangement will separate the family from superficially similar cucujoid groups e.g. Nitidulids. The basal segment is broad, large and visible from above but the insertions, on the side of the head in front of the eyes, are sometimes hidden. Eyes weakly to very strongly convex and protruding e.g. in Monotoma species. Pronotum elongate to quadrate, the surface smooth and punctured or, more usually, sculptured with depressions or carinae. Margins bordered, sometimes appearing serrate and/or with distinct tubercles at the angles. Scutellum large and obvious e.g. Rhizophagus or small and cryptic e.g. Monotoma. Elytra elongate and as long as, or longer than, the head and pronotum but there are exceptions. Generally with punctured striae or interstices, sometimes pubescent and this may be arranged randomly or in neat rows. Apices truncate, flatly rounded or separately rounded, generally leaving a part of the abdomen exposed, in many genera the last tergite is exposed in the female while the last two are exposed in the male. Abdomen with 5 visible articulated sternites, the first as long as the next 2 combined. The legs are generally short and robust with the tibiae often expanded apically and toothed externally. The tarsal formula varies from 5-5-5 to 4-4-4; in many the males are heteromerous, 5-5-4 while the females are 5-5-5. Many species show some degree of sexual dimorphism in the relative proportions of the head and pronotum while the middle and hind tibiae of males are often curved when compared to the females. In many species the shape of the terminal abdominal sternite differs between the sexes.

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Monotomid larvae are recognized by the presence of a pair of ventral epicranial ridges which run more or less parallel to the lateral margin of the head. , its presence separates the family from other cucujoid groups. They are elongate and cylindrical or rather flattened, parallel-sided and weakly sclerotized, generally pale yellow to white with the segment margins and the head darker. The head is round and sharply constricted to a narrow neck, and the mandibles are usually prominent. The legs are short. The 9th abdominal segment has setiferous tubercles and a pair of cerci or elongate processes. They occur in a wide range of situations; many are saproxylic or develop in decaying vegetation.