Deluge, in biblical history, flood of waters, described in Genesis 6-9, that inundated the entire earth or a large part of it. The only survivors were the occupants of the ark, a vessel with a beam of 26.7 m (87.5 ft) and a length of 160 m (525 ft), built by Noah at God's command. On the ark, besides Noah, were his wife, his three sons and their wives, and mated pairs of every species of animal. The narrative of the deluge in Genesis consists of two interwoven versions, the Yahwist and Elohist. Except on the reason for the flood, attributed in both to God's anger at humankind's wickedness, the two versions are frequently contradictory or divergent. According to the Yahwist sections of the narrative, for example, the flood is caused by a rain lasting 40 days. Noah sends out a raven at the end of this period, but it fails to return. He then releases a dove, which returns with an olive leaf. Sent out again seven days later, the dove does not return. Noah disembarks after another seven-day interval, builds an altar, and offers a sacrifice. God smells the “sweet savour” and promises not to destroy the world again. In the Elohist sections, the flood is accompanied by an upsurge of subterranean waters. It increases in intensity for 150 days, or five months of a solar year, and begins to recede in the seventh month. The ark then grounds “upon the mountains of Ararat.” On the first day of the next solar year, Noah leaves the ark and is blessed by God, who causes a rainbow as a sign of his covenant that such a flood will not occur again.

A number of ancient nations had folklore that predated the Bible and also made reference to the great flood. An example is the Gilgamesh Epic, an ancient Babylonian story dating from 2000bc and written on 12 cuneiform tablets. It concerns a ruler (Gilgamesh) who, after losing his dearest friend to a mysterious death, seeks out a wise man (Utnapishtim) who is a survivor of the great flood and knows the secret of immortality. Accounts such as this have intrigued biblical scholars because they lend further credence to the later biblical version. Although a number of these scholars have concluded that the biblical narrative is derived from the Babylonian story, it is possible that each was taken from a common earlier source, now lost.

Events similar to those described in the biblical story occur also in Greek mythology (see Deucalion). Among other peoples whose folklore and legends contain accounts of a devastating deluge are those of southern Asia, the aborigines of North, Central, and South America, and the natives of Polynesia. The Chinese and Japanese have stories of floods, but these do not, as a rule, destroy the entire earth. Curiously, flood legends do not occur among the ancient inhabitants of the Nile Valley and are not common anywhere else in Africa or in Europe.