The Sidewinder is the most common name of a species (Crotalus cerastes) of highly nocturnal rattlesnake found in the southwestern United States. It is also called the horned rattlesnake.

The sidewinder is named for its unusual form of movement across hot desert sands. It forms a letter-J shaped track as it moves via sidewinding, which allows it to move on the loose sand.

While the Sidewinder is venomous, its bite is not usually fatal to adult humans. However, the bite can cause severe systemic reactions and localized tissue death, and death is possible if the individual suffers an allergic reaction to the venom.

This snake is a pit viper, using its sensory pits to detect the infrared (heat) radiation of potential prey. The warhead and heat-seeking guidance system of the American-designed AIM-9 Sidewinder air-to-air missile (which is named for the snake) parallel the snake's venom and these sensory organs.

There are various subspecies:

• Crotalus cerastes cerastes, Mojave Desert Sidewinder
• Crotalus cerastes cercobombus, Sonoran Desert Sidewinder
• Crotalus cerastes laterorepens, Colorado Desert Sidewinder