Numerous meta-analyses have found Cognitive Behaviour Therapy for psychosis (CBTp) to be effective. The effect sizes that are achieved for positive symptoms in addition to antipsychotic treatment vary between small to medium. However, the effect sizes for changes in delusions are somewhat lower. Thus, it could prove beneficial to tailor CBTp interventions more precisely to the processes that are relevant to delusions. Empirically derived models of the formation and maintenance of delusions postulate an important role of cognitive biases, emotional factors and self-esteem. Additional studies have demonstrated the relevance of impaired sleep to delusions. Nevertheless, CBTp interventions that aim to change delusions tend to focus mainly on reasoning bias.