This paper attempts to summarize the evolution of interest in the concept of mentalization which has been researched and enriched by the linking of many disciplines alongside that of psychoanalysis and attachment theory. Taking into account the work of Professors Fonagy and Target and many others, the paper describes factors that enable the development of the capacity to mentalize and those that interfere. It will consider how the quality of attachment affects the transformation of pre-mentalized modes of experience to the recognition of psychic reality of self and other. While mentalizing is part and parcel of all therapies, a mentalization-based therapy was developed in the context of treatment of borderline personality disorder patients by Professors Bateman and Fonagy. The paper will illustrate key concepts in the theory of mentalization with the vignette taken from clinical practice.