Lycosuchidae is a family of therocephalians (an extinct type of therapsids, broader group which modern mammals belong to) known from fossils from what is now the Beaufort Group of South Africa and that lived during the Middle to Late Permian between roughly 265 to 259.2 million years ago. It currently includes only two genera each with a single species, Lycosuchus, represented by L. vanderrieti, and Simorhinella, represented by S. baini, both named by paleontologist Robert Broom in 1903 and 1915, respectively (though Simorhinella was not recognised as a lycosuchid until 2014). Both species are large predators characterised by their size, reduced tooth counts with large, almost "sabre toothed" canine teeth, and relatively short, broad and low snouts.

Lycosuchids were once thought to be defined by having two simultaneously functional pairs of canines, so-called "double canines", instead of a single pair of like in all other predatory therapsids (including predatory mammals). However, it has since been recognised that these actually represent overlap between an older pair and their alternated replacements in separate tooth sockets, and that fossils of lycosuchids with "double canines" in fact preserve teeth at different stages of growth and replacement. This is the same method of canine replacement used by other predatory therapsids, though the pattern appears to be unusual in lycosuchids as the alternating canines occur together more often compared to other predatory therapsids like other therocephalians and gorgonopsians.

Lycosuchids are among the earliest known therocephalians and are also thought to be the most basal. The Russian genus Gorynychus, containing two species, may also belong to the family, although this result is not typically recovered. Lycosuchids are only known from the upper Tapinocephalus and lower Endothiodon Assemblage Zones of the Karoo Basin, surviving the Capitanian mass extinction event between them that wiped out many other therapsid groups and ended the Middle Permian, but apparently only persisting as a "dead clade walking" that went extinct as ecosystems fully recovered, potentially competing with recently evolved large gorgonopsians.

Lycosuchids are characterised by several physical features of their skulls, including a low and wide snout that is proportionately short, typically half or less of the skull's whole length. The number of teeth are also distinctive, as lycosuchids only ever possess five or less incisors on each side of the upper jaw, a pair of canines, and very few postcanines behind them, typically only two or three behind each. In the lower jaws, there are only three incisors, a canine, and around five postcanines in each mandible.

While lycosuchids have shorter, wider and more robustly built snouts than early therocephalians in the family Scylacosauridae, they are nonetheless broadly similar to them, and in some ways also superficially resemble gorgonopsians. The large, almost "sabre-tooth" like canines are especially striking similarities. This anatomy suggests lycosuchids were capable of relatively strong bites with their large canines and incisors, and were resistant to the twisting of prey in their powerful jaws. All lycosuchids, including dubious genera and indeterminate specimens, are very similar superficially and share all of these features with little variation. The only accepted valid genera, Lycosuchus and Simorhinella, are mostly told apart by details of palate and the jaw joint.

Lycosuchids are large therocephalians, with the largest known Lycosuchus skull measuring almost 30 cm (12 in) long and the even larger skull of Simorhinella measuring 37 cm (15 in) long. The largest lycosuchid is an indeterminate specimen previously named as the holotype of "Scymnosaurus major" labelled SAM-PK-9005. It is a poorly preserved and incomplete snout measuring 22.6 cm (8.9 in) long, but proportionately it exceeds the snout dimensions of Simorhinella (which measures 18.2 cm (7.2 in) long). SAM-PK-9005 is both the largest known lycosuchid and also one of the largest therocephalians known altogether.

Little is known about the postcranial skeleton of lycosuchids, and there is little overlap in the available material to make broad statements about their anatomy. Nonetheless, two scapulae (shoulder blades) from different specimens both have a distinctive bony protuberance above the glenoid (shoulder joint), thought to be an enlarged attachment for the part of the triceps muscle. The ulna, known in both Simorhinella and SAM-PK-9005, is robust with a short olecranon process at the elbow, a feature probably related to their large size. A complete skeleton of a large therocephalian (UCMP 42667) that was previously described as a specimen of "Cynariognathus platyrhinus" (a taxon synonymous with Glanosuchus) in 1967 was alluded by palaeontologist Christian Kammerer to be a lycosuchid in a 2023 paper on scylacosaurid therocephalians, though it has yet to be compared in detail with other lycosuchid remains.

Historically, "double canines" in the upper jaw were regarded as the most defining trait of lycosuchids, and sometimes even the sole trait to distinguish them. Unlike other predatory therapsids (such as gorgonopsians and other therocephalians), which only ever have one functioning pair of upper canines at a time, lycosuchids were thought to have two distinct pairs, each with its own tooth socket (alveolus) one immediately behind the other, that were both simultaneously functional and independently replaced. Notably, these other therapsids also have two positions for each canine and the active tooth alternated between the alveoli every time it was replaced. The distinction made for lycosuchids was that two distinct sets teeth supposedly occupied both positions at the same time, rather than a single pair that alternated between them. This was thought to be a primitive characteristic retained by lycosuchids from earlier sphenacodont (or "pelycosaur") ancestors such as Dimetrodon, which were also thought to have two distinct sets of canines (now also known to be incorrect).