 This entry focuses on clinical delusions. Although the nature of delusions is controversial, delusions are often characterised as unusual beliefs that appear in the context of mental distress. Indeed, clinical delusions are a symptom of psychiatric disorders such as dementia and schizophrenia, and they also characterize delusional disorders. They can be associated with depression and obsessive compulsive disorder as well. The following case descriptions include an instance of erotomania, the delusion that we are loved by a person of higher status; an instance of Cotard delusion, the delusion that we are dead or disembodied; and a delusion of persecution, the belief that someone intends to cause us harm.