All snakes are members of the kingdom Animalia, the phylum Chordata, the class Reptilia and the order Squamata. The family, genus and species classifications differ for different kinds of snakes.
According to Reptile Knowledge, there are more than 20 different families of snakes, though the precise number is a matter of opinion. Depending on the system of classification used, between 2,900 and 3,400 different species of snake exist worldwide. Both snakes and lizards are members of the Squamata order, though snakes are often grouped in the suborder Serpentes. Scientists believe snakes descended from lizards. Pythons and boas still have tiny vestigial hind legs called "anal spurs."