Winnicott's theory of infant development is expanded to consider the unique psychic situation of twins. Two infants come into being in a matrix of relationships that is more complex than the single baby–mother unit. The mother of twins is preoccupied with each and both of her babies, and their internal worlds include a social context in addition to a sense of an individual self. Their formative experiences include conflicts between being primary and environmental, interrupted and an interruption. Because twins have equivalent and simultaneous psychic needs and their mother has one psychic apparatus, she experiences conflict when attending to either baby individually. Fathers of twins offer dyadic experiences that are less complex than the always triadic maternal relationship and these become critical in the twins' development of me/not me relations.