Vipera ammodytes, commonly known as horned viper, long-nosed viper, nose-horned viper, and sand viper, is a species of viper found in northern Italy, the Balkans, and parts of Asia Minor. Like all other vipers, it is venomous. It is reputed to be the most dangerous of the European vipers due to its large size, long fangs (up to 13 mm) and high venom toxicity. The specific name, ammodytes, is derived from the Greek words ammos, meaning "sand", and dutes, meaning "burrower" or "diver", despite its preference for rocky habitats. Five subspecies are currently recognized, including the nominate subspecies described here.

V. ammodytes grows to an average total length (snout-tail) of 85 cm (33.5 in), although individuals usually measure less than 75 cm (29.5 in). Maximum length also depends on locality, with northern forms distinctly larger than southern ones. In one field study on Golem Grad island (in North Macedonia), for example, females averaged 35 cm., and males at 37 cm.; the largest captured during the study was a male, at 66 cm. long. This indicates some degree of regional or insular dwarfism.

The head is covered in small, irregular scales, that are either smooth or only weakly-keeled; a pair of large supraocular scales also extends beyond the posterior margin of the eye. Ten to thirteen small scales surround each eye, and two rows separate the eye from the supralabials. The nasal scale is large, single (rarely divided), and separated from the rostral by a single nasorostral scale. The rostral scale is wider than it is long.

The most distinctive characteristic is a single "horn" on the snout, just above the rostral scale. It consists of approximately nine to seventeen small scales, arranged in two (occasionally three or four) transverse rows. It grows to a length of about 5 mm (0.20 in) and is actually soft and flexible. In southern subspecies, the horn sits vertically upright, while in V. a. Ammodytes it points diagonally forward.

The body is covered with strongly keeled dorsal scales, in 21 to 23 rows (rarely 25), at mid-body. The scales bordering the ventrals are smooth or weakly-keeled. Males have anywhere from 133 to 161 ventral scales and 27 to 46 paired subcaudals, whereas females have anywhere from 135 to 164, and 24 to 38, respectively. The anal scale is single.

The color pattern is different for males and females. In males, the head has irregular dark brown, dark gray, or black markings. A thick, black stripe runs from behind the eye to behind the angle of the jaw. The tongue is usually black, and the iris has a golden or coppery color. Males have a characteristic dark blotch or V marking on the back of the head that often connects to the dorsal zigzag pattern. The ground color for males varies and includes many different shades of gray, sometimes yellowish or pinkish gray, or yellowish brown. The dorsal zigzag is dark gray or black, the edge of which is sometimes darker. A row of indistinct, dark (occasionally yellowish) spots runs along each side, sometimes joined in a wavy band.

Females have a similar color pattern, except that it is less distinct and contrasting. They usually lack the dark blotch or V-shaped marking (on the back of the head) that the males have. Ground color is variable, and tends more towards browns and bronzes; grayish-brown, reddish-brown, copper, "dirty cream", or brick red. The dorsal zigzag is a shade of brown.

Both sexes have a zigzag dorsal stripe, set against a lighter background. This pattern is often fragmented. The belly color varies, and can be grayish, yellowish-brown, or pinkish and "heavily clouded", or with dark spots. Sometimes, the ventral color is black or bluish gray, with white flecks and inclusions edged in white. The chin is lighter in color than the belly. Underneath, the tip of the tail may be yellow, orange, orange-red, red, or green. Melanism does occur, but is rare. Juvenile color patterns are about the same as the adults. The cinderella snake may be between the rail and a ballast prism, accumulating solar heat in her body.