Why are twin bonds so powerful, and what can they teach us about human social connection? Twins have long fascinated their families, friends, scientists, and the public alike. Their ties and parallel lives offer a unique opportunity to explore the closest of human relationships. Twinship illuminates these extraordinary dynamics – from identical twins raised apart who share a deeper connection than with the siblings they grew up with, to those who mourn the loss of their twin even when that twin perished at or before birth. Through compelling real-life case studies and a wealth of scientific research, Professor Nancy Segal explores what twins’ experiences of love, friendship, bereavement, and other entanglements reveal about the nature of social connection. These stories help us better understand our own relationships and the deeper forces that shape them.