The aim of the present dissertation project was to investigate several hypotheses of psychological models that explain the development and maintenance of persecutory delusions in patients with schizophrenia-spectrum disorders (Garety et al., 2001; Freeman et al., 2002). Recent psychological models emphasize the role of specific social-cognitive and emotional biases in the generation and maintenance of persecutory delusions and positive symptoms of schizophrenia. One social-cognitive bias is the tendency of patients with persecutory delusions to attribute negative events towards external factors (other persons/fate). Deficits in Theory of Mind (ToM; Premack; Woodruff, 1978), the ability to infer the intentions, thoughts, emotions and behaviour of other persons, are also subsumed to the social-cognitive biases, as well as the tendency to "jump to conclusions", to gather little data before reaching a decision. Moreover, negative self-schemata, anxiety and depression are subsumed to the emotional factors that influence the development and maintenance of persecutory delusions. According to these hypotheses, cognitive-behavioural interventions were adapted in order to modify and reduce these biases in order to ameliorate patients delusions and to enhance their quality of life. Several empirical studies report the effectiveness of cognitive-behavioural therapy in schizophrenia (Wykes et al., 2008). However, the specific processes through which the social-cognitive and emotional biases influence the generation and maintenance of delusions are still unknown. Thus, the aim of the present dissertation project was to investigate underlying mechanisms of social-cognitive and emotional biases in order to improve the development of cognitive-behavioural interventions for patients with schizophrenia in an effort to provide a basis of knowledge by which present interventions can be modified and adapted to the specific problems of these patients. In a cross-sectional design, 63 patients with schizophrenia-spectrum disorders are compared to 63 non-clinical controls. The first aim of the present study was to test whether patients with acute persecutory delusions presented a self-decreasing implicit attribution style (AS) and an implicit low self-esteem. A modified assessment of implicit AS was introduced, which offered three attributional loci (internal, external-personal and external-situational) instead of two as in previous studies. Compared to patients with remitted persecutory delusions and non-clinical controls, patients with acute persecutory delusions showed a self-decreasing implicit attributional style: They attributed negative events towards themselves and positive events towards situational factors, whereas their explicit self-serving AS was comparable to controls. Patients implicit self-decreasing AS was associated with low implicit self-esteem. In addition, deluded patients presented an unstable self-esteem (low explicit and normal implicit self-esteem). The second aim was to investigate the association between one specific aspect of ToM, the ability to infer other people s intentions and delusions of persecution. A new ToM movie paradigm developed in the present study was introduced: Movies of social situations were presented and participants were required to answer questions with regard to the intentions and emotions of the characters in the movies. Patients with persecutory delusions were specifically impaired in the ability to infer the intentions of other persons compared to patients with remitted persecutory delusions and non-clinical controls. Furthermore, results indicate an association between deficits in the ability to infer intentions and delusions in general, even after controlling for executive functioning. The third aim was to test whether deficits in ToM and deficits in the recall of autobiographical memories are associated with problems in social performance in patients with schizophrenia-spectrum disorders. Results indicate that deficits in the ability to infer other people s emotions in social situations and in the recall of autobiographical memories are associated with deficits in social performance. The ToM ability to infer emotions and the ability to recall autobiographical memories were better predictors of social performance than psychopathological symptoms and other neuro-cognitive deficits. In sum, the dissertation project contributes important conclusions with regard to psychological models on the development and maintenance of persecutory delusions and the mediating influence of social-cognitive biases and emotional factors. Results emphasize how important it is to develop and modify specific cognitive-behavioural interventions that improve social-cognitive abilities and emotional problems in patients with persecutory delusions.