Mentalizing - the ability to understand oneself and others by inferring the mental states that lie behind overt behavior - develops during childhood within the context of a secure attachment relationship. It is crucial to self-regulation and constructive, intimate relationships. Failure to retain mentalizing, particularly in the midst of emotional interactions, is a core problem in borderline personality disorder and results in severe emotional fluctuations, impulsivity, and vulnerability to interpersonal and social interactions. Mentalization-based treatment for borderline personality disorder is a 'How to Do It' book outlining a clinically proven treatment for Borderline Personality Disorder. Containing illustrative clinical examples, it details precisely how to develop and implement treatment and is a companion to the highly successful book Psychotherapy for Borderline Personality Disorder - mentalization based treatment. This practical guide explains how to treat borderline patients by helping them develop a more robust mentalizing capacity within the context of an attachment relationship. It provides the practitioner with everything they need to know about how to practise mentalizing treatment in day patient and out-patient settings. Enough theory is provided to orientate the clinician and there is step-by-step practical advice on the assessment of mentalizing and interpersonal relationships, how to structure treatment, the use of basic mentalizing interventions and how to apply them, as well as information on what not to do. In addition, it includes a check list to be used in the assessment of mentalizing and a self-rating exercise for practitioners to evaluate their adherence to mentalizing.