The skull is usually sturdy and has a short facial region. Enhydra is the only genus with 2 lower incisors. The incisors of mustelids are not specialized, the canines are elongate, the premolars are small and sometimes reduced in number, and a constriction is usually present between the lateral and medial halves of the upper molar. The carnassials are developed. The second lower molar, if present, is reduced to a simple peg.
Mustelids are either nocturnal or diurnal and often shelter in crevices, burrows, and trees.
Badgers usually dig elaborate burrows. Mustelids move about on their digits, or partly on their digits and partly on their soles. The smaller, slender forms usually travel by means of a scampering gait interspersed with a series of bounds. The larger, stocky forms proceed in a slow, rolling, bearlike shuffle. Mustelids often sit on their haunches to look around.