Why do twins remain uncanny to those born alone-in other words, most of us? Even with the rise of IVF and an increase in multiple births, why do we still do “a double take” when we encounter twins? Why has this been a near-universal response throughout human history, and how has it played out in religion and myth? Through the work of leading scholars in religion, folklore and mythology, history, anthropology, and archaeology, explores how twinship has long been imagined, especially in the complex relationship of sacred twin traditions to “twins on the ground” in biology and lived experience. The book considers the multiple ways in which the “doubling” of a human being may be interpreted as auspicious and powerful-or suppressed as unstable and dangerous. Why has this been so and how does it affect living twins today? Treating both famous and lesser-known twins-including supernatural animal twins-in the ancient Near Eastern and classical Mediterranean worlds; early Christianity and Gnosticism; Vedic, Hindu, West African, Black Atlantic, and native American traditions; ancient Mesoamerica, Celtic Roman Britain, and Scandinavia; and in the special, fraught bond shared by all twins, the book offers a variety of perspectives on this topic of great cultural significance.