In this discussion, I note that four articles in this issue illustrate common themes about twinship. They describe Kohut's approach that evolved from a more restricted definition of dyadic commonality, to a more general definition of being a “human among humans.” The authors illuminate the significance for adaptive development of twinship experiences that include both sameness and difference. Clinical examples are presented that illustrate the rigidification and concretization of sameness or difference that results from trauma.