Snakes have long been grouped into families within Alethinophidia based on their morphology, especially that of their teeth.

More modern phylogenetic hypotheses using genetic data[2][3][4][5][6][7][8][9][10][11][excessive citations] support the recognition of 19 extant families (see below), although the taxonomy of alethinophidian snakes has long been debated, and ultimately the decision whether to assign a particular clade to a particular Linnaean rank (such as a superfamily, family, or subfamily) is arbitrary.

[1] Coniophis presents the vertebral morphology similar to modern-day Aniliidae.

The family Nigerophiidae includes both aquatic[1] Nubianophis from Wadi Abu Hashim and Nigerophis from the Palaeocene of Niger.

[1] The extinct marine Simoliophidae are known from the Cenomanian of North Africa, the Middle East, and Eastern Europe, indicating a Tethyan distribution; they are notable for preserving evidence of vestigial hindlimbs.