Facing the other in the guise of twin or double, one might sense a threat to the idea of personal identity, yet people are teased and delighted by the odd prospect of becoming otherwise. Twins arouse a sense of awe in many societies around the world. Jacob and Esau, Horus and Set, Jekyll and Hyde - all these and many more are recurrent pairs who lure us into the world found through the looking glass. The author sets out to bring together genetics, psychology, mythology and art in order to clarify the lore and reveal the enigma of the dyadic principle, common to modern and archaic intuition alike. John Lash established the Institute for Creative Mythology at Santa Fe, New Mexico, in 1981.