This thesis examines the role of adult attachment style on the internalisation of stigma amongst adults affected by mental health problems in the United Kingdom. A systematic review, completed for this thesis, on the role of social and relational factors in internalised stigma found strongest evidence for a negative association between social support and internalised stigma. Just one eligible study considered the role of attachment style. In the empirical study, a transdiagnostic sample with experience of recent secondary mental health service use (n = 122) completed an online cross-sectional survey with measures of internalised and perceived public stigma, adult attachment style, self-esteem, mood and functioning. Correlation analysis tested whether internalised stigma and perceived public stigma were significantly positively correlated (hypothesis one). Hierarchical multiple regression tested whether anxious and avoidant attachment styles were positively associated with a significant amount of variance in internalised stigma when controlling for other variables (hypotheses two and three). Regression-based moderation analysis tested whether the relationship between perceived public stigma and internalised stigma was moderated by anxious and avoidant attachment styles (hypotheses four and five). Results indicated that internalised stigma, perceived public stigma and insecure attachment were common in this sample. Internalised stigma was positively associated with perceived public stigma but neither anxious or avoidant attachment were associated with a significant amount of variance in internalised stigma when controlling for other variables. Similarly, no moderating effect on the relationship between perceived public stigma and internalised stigma was found for insecure attachment. Limitations, which may have contributed towards the failure to find some predicted effects, are discussed. Implications for policy and practice are also discussed and recommendations are made for future research. It is concluded that despite these mixed results further research on the role of attachment style in internalised stigma is warranted.