The Book of Enoch is an ancient Hebrew apocalyptic religious text, ascribed by tradition to the patriarch Enoch who was the great-grandfather of Noah. The Book of Enoch contains unique material on the origins of demons and Nephilim, why some angels fell from heaven, an explanation of why the Genesis flood was morally necessary, and prophetic exposition of the thousand-year reign of the Messiah. 

The Book of Enoch tells of the Nephilim and the reason for the great flood of Noah.

Although recognized only by the Ethiopian Church as canon, the book of Enoch was familiar to the Apostles and 1 Enoch 1:9 is quoted by Jude. Jude 1:14-15 King James Version (KJV) 14: And Enoch also, the seventh from Adam, prophesied of these, saying, Behold, the Lord cometh with ten thousands of his saints, 15: To execute judgment upon all, and to convince all that are ungodly among them of all their ungodly deeds which they have ungodly committed, and of all their hard speeches which ungodly sinners have spoken against him.

This 1882 translation from Rev. George H. Schodde PhD. has been reproduced, complete with all explanatory notes from the translator.