Individuals who devalue themselves due to their body size are said to hold internalised weight stigma (IWS). IWS has received increased research attention in recent years, with studies highlighting its links to a multitude of adverse physical and mental health outcomes (Pearl & Puhl, 2018). Despite such advances, the specific mechanisms by which IWS affects health are under-researched. Moreover, there is a lack of consensus around the conceptualisation of IWS (Romano et al., 2022), and there is a need for further research within this field. Part A of this portfolio consists of an empirical study designed to examine whether dichotomous thinking – a cognitive distortion whereby an individual processes the world through binary categories - mediates the relationship between IWS and mental health outcomes in adults who are overweight or obese. Participants were asked to complete four validated questionnaires on an online platform at a single time-point. Mediation analysis indicated that dichotomous thinking fully mediates the relationship between IWS and anxiety, and partially mediates the relationship between IWS and both depression and impairment in functioning. Part B consists of a second empirical paper which aimed to understand the psychological process through which IWS becomes internalised amongst those who are overweight or obese using a combination of two qualitative research approaches: Interpretative Phenomenological Analysis (IPA; Smith, Flowers, & Larkin, 2021), and Photovoice (Wang, Yi, Tao, & Carovano, 1998). Participants were asked to complete a photography task where they captured situations in which they experienced weight stigma over a two-week period; they were then invited to discuss their pictures in a 60-minute interview. Analysis of interview data using IPA identified four processes as contributors of IWS: the self-application of stigmatised narratives, ascribing to an undesired fat identity, experiencing a socially focused anxiety response, and psychological distress managed through unhelpful coping behaviours.