Skinks are lizards that comprise all species within the family Scincidae, which is part of the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. Skinks are characterized by their smaller legs in comparison to typical lizards and are found in different habitats except arctic and subarctic regions.

The word skink, which entered the English language around 1580–1590, comes from classical Greek skinkos and Latin scincus, names that referred to various specific lizards.

Skinks look like lizards of the family Lacertidae (sometimes called true lizards), but most species of skinks have no pronounced neck and relatively small legs. Several genera (e.g., Typhlosaurus) have no limbs at all. This is not true for all skinks, however, as some species such as the red-eyed crocodile skink have a head that is very distinguished from the body. These lizards also have legs that are relatively small proportional to their body size.

Skinks' skulls are covered by substantial bony scales, usually matching up in shape and size, while overlapping. Other genera, such as Neoseps, have reduced limbs and fewer than five toes (digits) on each foot. In such species, their locomotion resembles that of snakes more than that of lizards with well-developed limbs. As a general rule, the longer the digits, the more arboreal the species is likely to be. A biological ratio can determine the ecological niche of a given skink species. The Scincidae ecological niche index (SENI) is a ratio based on anterior foot length at the junction of the ulna/radius-carpal bones to the longest digit divided by the snout-to-vent length.

Most species of skinks have long, tapering tails they can shed if predators grab onto them. Such species generally can regenerate the lost part of a tail, though imperfectly. A lost tail can grow back within around three to four months. Species with stumpy tails have no special regenerative abilities.

Some species of skinks are quite small; Scincella lateralis typically ranges from 7.5 to 14.5 cm (3 to 5+3⁄4 in), more than half of which is the tail. Most skinks, though, are medium-sized, with snout-to-vent lengths around 12 cm (4+1⁄2 in), although some grow larger; the Solomon Islands skink (Corucia zebrata) is the largest known extant species and may attain a snout-to-vent length of some 35 cm (14 in).

Skinks can often hide easily in their habitat because of their protective colouring (camouflage).

Skinks in the genus Prasinohaema have green blood because of a buildup of the waste product biliverdin.