Rattlesnakes are a group of venomous snakes of the genera Crotalus and Sistrurus of the subfamily Crotalinae (the pit vipers). The 36 known species of rattlesnakes have between 65 and 70 subspecies, all native to the Americas, ranging from southern Alberta and southern British Columbia in Canada to central Argentina.

Rattlesnakes are predators that live in a wide array of habitats, hunting small animals such as birds and rodents.

The threat of envenomation, advertised by the loud shaking of the titular noisemaker ("rattle") at the end of their tails, deters many predators. However, rattlesnakes fall prey to hawks, weasels, king snakes, and a variety of other species. Rattlesnakes are heavily preyed upon as neonates, while they are still weak and mentally immature. Large numbers of rattlesnakes are killed by humans. Rattlesnake populations in many areas are severely threatened by habitat destruction, poaching, and extermination campaigns.

Rattlesnake bites are the leading cause of snakebite injuries in North America. However, rattlesnakes rarely bite unless provoked or threatened; if treated promptly, the bites are rarely fatal.