Family therapy for adolescent anorexia nervosa (FT-AN) is the first line treatment for the disorder, but little is known about who the treatment works for, or how it works. This thesis investigates the potential value of the constructs of attachment and mentalization as predictors of outcome in family therapy for adolescent AN. The thesis presents a systematic review of attachment and mentalization and their association with child and adolescent eating pathology in which 22 relevant studies were found. In keeping with the evidence base for adults with eating disorders, both attachment and mentalization were found to be correlates of eating pathology in childhood and adolescence. However, evidence for these constructs in the process of treatment in child and adolescent eating disorders is scarce. In a second systematic review, the psychometric properties of attachment measures in middle childhood and adolescence were investigated across 53 studies. The overall conclusion of the study is that there is a lack of evidence of adequate psychometric properties for attachment measures in this age group.In the main study, attachment and mentalization were investigated as predictors of outcome in a sample of adolescents and their parents (n = 192) receiving FT-AN across three specialist outpatient eating disorder services. Mentalization, but not attachment, was found to predict poor clinical outcome at nine months after starting of treatment, with the strongest predictive effect being excessive certainty about mental states as assessed in parents. Therapeutic alliance scores at one month were predictive of outcome but did not play a mediating role in relation to baseline attachment or mentalization. In a further empirical study, definitions of eating disorder recovery were investigated through a qualitative analysis of comments on recovery-focused social media forums. Two super-ordinate themes emerged: firstly, recovery was defined as encompassing broad psychosocial domains of wellbeing; secondly, recovery was understood to be an ongoing process. Social connectedness to others was regarded as important both to the process and definition of eating disorder recovery. The final chapter of the thesis integrates findings from across the studies with emerging theoretical developments in the fields of attachment and mentalization. It is argued that attachment and mentalization represent worthwhile constructs for further FT-AN research, with a particular emphasis on the need to better understand the mechanisms by which excessive mental state certainty might lead to poor clinical outcomes.