Adder, the name of several snakes, including many European vipers and harmless North American snakes. The common adder is another name for the common European viper. Also called adder is the copperhead. Puff adder is a name applied to the true puff adder and to the harmless hognose snake. The milk snake sometimes is called an adder; the water moccasin, the water adder.

Night adders form a genus of primitive true vipers. These nocturnal snakes live in Africa south of the Sahara. The death adder of Australia is a venomous snake that resembles a viper.

The four species of night adders form the genus Causus of the viper family, Viperidae. The death adder is Acanthophis antarcticus of the cobra and coral snake family, Elapidae.

Most adders are in the family Viperidae. The European viper is classified as Vipera berus. The puff adder is Bitis arietans. The death adder belongs to the family Elapidae. It is classified as Acanthophis antarcticus. Hognose snakes belong to the family Colubridae and the genus Heterodon.