Genesis 6.1-4 contains one of the strangest accounts in the Bible. Sons of god have sex with human women. Creatures called Nephilim are produced, who elsewhere are described as Giants.
In his April 2019 article for Bible and Interpretation, Jaap Doedens outlines the major alternatives for interpreting this odd passage. The article is based on his book, The Sons of God in Genesis 6:1–4: Analysis and History of Interpretation (Old Testament Studies 76.Leiden: Brill, 2019).