At the origin of the Watchers tradition is the single enigmatic reference in Genesis 6 to the "sons of God" who had intercourse with human women, producing a race of giants upon the earth. That verse sparked an explosion of cosmological and theological speculation in early Judaism. Here leading scholars explore the contours of the Watchers traditions through history, tracing their development through the Enoch literature, Jubilees, and other early Jewish and Christian writings. This volume provides a lucid survey of current knowledge and interpretation of one of the most intriguing theological motifs of the Second Temple period.