Over history three main theories are advanced to explain this. The first theory is the “sons of god” are fallen angels and the daughters of men are mortals. This ancient viewpoint hinges in part on the assumption that Jude 1:6-7 refers to these angels. If this sin is perpetuated by angels then why is man punished in the flood? Christ said in Matthew 22:30 that angels do not marry. There is some difficulty in understanding mortals as descendants of angels and not from Adam.(Acts 17:26) The second theory is that the “sons of god” are from the Godly line of Seth while the “daughters of men” are of the line of Cain. The sin which they are charged is common to the whole scripture, especially the Pentateuch; the intermarriage of the chosen people of God with those who are unholy. How can these men be considered holy when the Bible states only Noah was holy. (Genesis 6:8-9) Why is the “sons of god” not used with this meaning in any other place? Why only sons and not daughters are associated with the line of Seth? The last theory is very popular among conservatives. Recent archaeological evidence suggests that the term “sons of god” was sometimes used to describe kings (Exodus 21:6, 22:8, Psalm 82:6-7) Therefore the ‘sons of god” are immoral kings who use their power to take women and use them at their will. Well pick your pleasure or poison on your choice here? Regardless these were acts of immorality. Who are the “sons of god” today? Who are the “daughters of men” today? God has sons and daughters! Who are the sons and daughters of men today? The sons and daughters of god are those who have accepted Jesus Christ into their lives! Born gain! The sons and daughters of men are those who have only had the first birth or natural birth and not the second birth! They have either rejected Christ or are living out of ignorance or do not have the knowledge and revelation about Him. Thankyou. James and Hamsa Sasse. GodWhoisGod.com