Pregnancies after loss are often characterized by feelings of depression, anxiety, trauma-like symptoms, and problems bonding to the fetus. Difficulties bonding to the unborn baby during pregnancy are of clinical importance because they are predictive of problems in the mother–infant attachment relationship, perhaps explaining why some studies show a higher risk of insecure attachment for babies born after loss. O’Leary (2004) has proposed that problems in prenatal bonding during pregnancies after loss are the result of the challenge these mothers face of having to grieve the loss of one baby while bonding to another. This article argues that the theory of mentalization helps to explain why some parents successfully resolve this central challenge during pregnancies after loss and go on to develop a secure attachment to the next infant, whereas others continue to experience long-term attachment problems. Specifically, pregnancies after loss are conceptualized as a potentially traumatic experience in which mentalization may decrease and, at the same time, serve as a protective factor against attachment problems with infants born after loss due to unresolved trauma and grief. Several aspects of mentalization, including the capacity to mentalize: (a) affect associated with trauma and loss, (b) attachment relationships as distinct, (c) multiple and conflicting mental states, and (d) early inadequate attachment experiences related to trauma and loss, are proposed to help mothers pregnant after loss to mourn the loss of one baby while attaching to another, ameliorating potential attachment problems postpartum. Clinical interventions for facilitating these mentalizing capacities are suggested.