Before the Great Flood, the Book of Genesis tells us that "the sons of God" mated with "the daughters of men." From this illicit union, came the "giants, mighty men of renown." This enigmatic passage has captivated the imagination of both Rabbinic scholars and Church Fathers for millennia. Who were these "giants" (also known as Nephilim)? The author examines the three major hypotheses which have been postulated and offers his own explanation as to their origin.