This study examines the effectiveness of collaborative case conceptualisation (CCC), a novel assessment approach, compared to standard assessment as usual (AAU), for adults with Anorexia Nervosa. Participants will be randomly allocated to one of these two assessment approaches. Participation will involve attending up to 5 assessment sessions which will last approximately 1 hour each, and completing a questionnaire package before, immediately after, and 12 months after the assessments. Assessment will be conducted at Australian Catholic University and ongoing medical monitoring will be conducted by BETRS and community treatment teams. Results of this study will inform the development of assessment processes to maximise treatment engagement and retention for adults with Anorexia Nervosa.