The angels might refer to the fall of Satan and the angels who followed him, but no Old Testament passage clearly describes this event (see study notes on Isaiah 14:12–17; Ezekiel 28:12–19). Jude was probably referring to Genesis 6:1–4. Jewish tradition understood the “sons of God” in Genesis 6 to be wicked angels. They believed God punished these angels because they had sexual relations with women (see 1 Enoch 6–10; see also study notes on 1 Peter 3:19–20; 2 Peter 2:4). Jude later (in verses 14–15) quotes directly from 1 Enoch.