The antediluvian period was the period that preceded the Great Flood of Noah as related in the Book of Genesis in the Hebrew Bible. It was an important feature in versions of natural history that were formerly much more widely accepted, but still taught at websites like 'Answers in Genesis (http://answersingenesis.org)'. The primary source of knowledge about the antediluvian period is Genesis, chapters 5 and 6.

The Bible speaks of this era as being a time of great wickedness. There were Gibborim (giants) in the earth in those days as well as Nephilim, some translations identify the two as one and the same. These giants were the offspring of the "sons of God", usually interpreted as angels, who descended from the heavens to beget them with mortal women. The Gibborim were unusually powerful; Genesis calls them "heroes of old, men of renown;" (Enoshi Ha Shem). Genesis also says at that time mankind was an evil race, whom God repented of creating, and therefore he sent the Flood to wipe out all human life, all except Noah and his family. Nevertheless, the Nephilim (literally meaning fallen ones) reappear much later in the Biblical narrative, in Numbers 13:31-33.

The Gibborim, and the Flood, were once considered to be the source of large fossil bones, and the explanation of how seashells and other traces of marine life came to be found in rocks on mountaintops. Evidence of large extinct forms of life were thought to have been the remnants of large creatures exterminated together with the race of giants.

The antediluvian patriarchs were credited with unusually long lifespans in the Book of Genesis. These include:

• Adam 930 years (begat at 130 years)
• Seth 912 years (begat at 105 years)
• Enosh 905 years (begat at 90 years)
• Kenan 910 years (begat at 70 years)
• Mahalalel 895 years (begat at 65 years)
• Enoch 365 years (begat at 65 years)
• Jared 962 years (begat at 62 years)
• Methuselah 969 years (begat at 187 years)
• Lamech 777 years (begat at 82 years)
• Noah 950 years (begat at 500 years)

"Antediluvian" is sometimes used figuratively to refer to anything of great age.

In Vampire:_The_Masquerade the Antediluvians are the most ancient of vampires, who have remained in hiding or suspended animation from the time of the flood of Noah. Their return is a sign of the end times.