They are mentioned in Gen. 6. They were people of great size and strength. The Hebrew meaning of Nephilim means "fallen ones". In men's eyes, they were seen as heroes and men of renown, but in Gods eyes, they were seen as wicked men , or sinners(fallen ones), and ripe for swift judgment. They were not angels, as some people suppose, but only men. This scripture has been very badly misinterpeted.If you study it out, you have to study the hebrew meaning of each word.