This article explores the meaning and significance of the notion of mentalization. Although Fonagy borrows the concept from theory of mind, he develops it in a way that has particular relevance for the integration of attachment theory and psychoanalytic theory. Mentalization is not innate, but has its source in the early relationship wherein the primary caregiver's interpretation of the infant allows the infant's mind to grow and interpret for himself or herself; it is not just cognitive, but is based on cognitive-affective schemas; and it is not just about correct social prediction, but is especially germane to the kind of mindreading that occurs in the context of intimate relationships such as psychotherapy. I introduce a new criticism of the theory of mind literature as ignoring that minds have emotional styles, and I use Balint's distinction between philobats and ocnophils to illustrate this point. Finally, I explicate the concept of mentalized affectivity and propose that it allows us to capture how minds can understand one another in the clinical realm.