Serpents (Hebrew: נָחָשׁ, romanized: nāḥāš) are referred to in both the Hebrew Bible and the New Testament. The symbol of a serpent or snake played important roles in the religious traditions and cultural life of ancient Greece, Egypt, Mesopotamia, and Canaan. The serpent was a symbol of evil power and chaos from the underworld as well as a symbol of fertility, life, healing, and rebirth.

Nāḥāš (נחש‎), Hebrew for "snake", is also associated with divination, including the verb form meaning "to practice divination or fortune-telling". Nāḥāš occurs in the Torah to identify the serpent in the Garden of Eden. Throughout the Hebrew Bible, it is also used in conjunction with seraph to describe vicious serpents in the wilderness]. The tannin, a dragon monster, also occurs throughout the Hebrew Bible. In the Book of Exodus, the staves of Moses and Aaron are turned into serpents, a nāḥāš for Moses, a tannin for Aaron. In the New Testament, the Book of Revelation makes use of ancient serpent and the Dragon several times to identify Satan or the Devil (Revelation 12:9; 20:2). The serpent is most often identified with the hubristic Satan, and sometimes with Lilith.

The narrative of the Garden of Eden and the fall of humankind constitute a mythological tradition shared by all the Abrahamic religions, with a presentation more or less symbolic of Abrahamic morals and religious beliefs, which had an overwhelming impact on human sexuality, gender roles, and sex differences both in the Western and Islamic civilizations. In mainstream (Nicene) Christianity, the doctrine of the Fall is closely related to that of original sin or ancestral sin. Unlike Christianity, the other major Abrahamic religions, Judaism and Islam, do not have a concept of "original sin", and instead have developed varying other interpretations of the Eden narrative.^{[excessive citations]}

In the Hebrew Bible, the Book of Genesis refers to a serpent who triggered the expulsion of Adam and Eve from the Garden of Eden (Gen 3:1–20). Serpent is also used to describe sea monsters. Examples of these identifications are in the Book of Isaiah where a reference is made to a serpent-like dragon named Leviathan (Isaiah 27:1), and in the Book of Amos where a serpent resides at the bottom of the sea (Amos 9:3). Serpent figuratively describes biblical places such as Egypt (Jer 46:22), and the city of Dan (Gen 49:17). The prophet Jeremiah also compares the King of Babylon to a serpent (Jer 51:34).

The Hebrew word נָחָשׁ (Nāḥāš) is used in the Hebrew Bible to identify the serpent that appears in Genesis 3:1, in the Garden of Eden. In the first book of the Torah, the serpent is portrayed as a deceptive creature or trickster, who promotes as good what God had forbidden and shows particular cunning in its deception. (cf. Genesis 3:4–5 and 3:22) The serpent has the ability to speak and to reason: "Now the serpent was more subtle (also translated as "cunning") than any beast of the field which the Lord God had made". There is no indication in the Book of Genesis that the serpent was a deity in its own right, although it is one of only two cases of animals that talk in the Torah (Balaam's donkey being the other).

God placed Adam in the Garden of Eden to tend it and warned Adam not to eat the fruit of the Tree of Knowledge of Good and Evil, "for in the day that thou eatest thereof thou shalt surely die." The serpent tempts Eve to eat of the tree, but Eve tells the serpent what God had said. The serpent replies that she would not surely die (Genesis 3:4) and that if she eats the fruit of the tree "then your eyes shall be opened, and ye shall be as gods, knowing good and evil." (Genesis 3:5) Eve ate the fruit, and gave some to Adam who also ate. God, who was walking in the Garden, learns of their transgression. To prevent Adam and Eve from eating the fruit of the Tree of Life and living forever, they are banished from the garden upon which God posts an angelic guard. The serpent is punished for its role in the Fall, being cursed by God to crawl on its belly and eat dust.

There is a debate about whether the serpent in Eden should be viewed figuratively or as a literal animal. According to one midrashic interpretation in Rabbinic literature, the serpent represents sexual desire; another interpretation is that the snake is the yetzer hara. Modern Rabbinic ideas include interpreting the story as a psychological allegory where Adam represents reasoning faculties, Eve the emotional faculties, and the serpent the hedonic sexual/physical faculties. Voltaire, drawing on Socinian influences, wrote: "It was so decidedly a real serpent, that all its species, which had before walked on their feet, were condemned to crawl on their bellies. No serpent, no animal of any kind, is called Satan, or Belzebub, or Devil, in the Pentateuch."

20th-century scholars such as W. O. E. Oesterley (1921) were cognizant of the differences between the role of the Edenic serpent in the Hebrew Bible and its connections with the "ancient serpent" in the New Testament. Modern historiographers of Satan such as Henry Ansgar Kelly (2006) and Wray and Mobley (2007) speak of the "evolution of Satan", or "development of Satan".