This family contains 8 described Recent genera , only 4 of which still survive, and 33 species. The pelage is harsh in hutias but soft and thick in the nutria.
Coloration is generally brownish or grayish.
The head is broad in hutias and somewhat triangular in the nutria. All genera have a robust body form, small eyes and ears, short limbs, a reduced thumb, and prominent claws. There are two pairs of mammae in female hutias and four pairs in the female nutria. In hutias the incisors are narrow, and the rootless cheek teeth are high-crowned and grow throughout life. In the nutria the incisors are broad and strong, and the extremely high-crowned cheek teeth are semirooted and decrease in size as they converge anteriorly.