This thesis examines the role of self-concept in cognitive models of persecutory delusions. It consists of two sections: A literature review and an empirical research paper. The literature review examines the.role of self-concept in the formation and maintenance of persecutory delusions as proposed by the three main cognitive models; the attribution self-representation model, persecutory and punishment types of paranoia, and the threat anticipation cognitive model. Each model makes different predictions about the role of self-concept, in particular self-esteem and self-schemas. The review concludes that, in terms of the current research evidence, there is broad support for the threat anticipation cognitive model of persecutory delusions. However, further research evidence is needed to fully clarify the role of self-concept in persecutory delusions. The empirical study investigates the predictions of the attribution self- representation model in a clinical group of people with persecutory delusions in comparison with a healthy control group. Persecutory delusions are predicted to defend against low implicit self-esteem reaching conscious awareness. For people with persecutory delusions, the model predicts lower levels of implicit self-esteem and equivalent levels of explicit self-esteem when compared with a healthy control group. The results of this study do not support the attribution self-representation model. The findings of this study are discussed in relation to other cognitive models of persecutory delusions and areas for further research are highlighted.