The types of symptom that have been grouped together, by psychiatric convention, under the term ‘psychosis’ are those which suggest that the person does not have the same sense of reality as most of those around them. They experience hallucinations and/or delusions. Two main groupings are usually identifi ed – the affective and non-affective psychoses, the former where extremes of mood are prominent features, the latter where in fact the emotions may be ‘fl attened’. Manic depression and schizophrenia are the two labels with which most people will be familiar, diagnosing conditions that can sometimes be quite diffi cult to distinguish, particularly in a fi rst episode, as there are overlapping symptoms. Both are ‘functional psychoses’ where no medical explanation (such as fever, brain damage or drug misuse) appears to account for the symptoms. This chapter will focus primarily on research on the latter – the non-affective psychoses, particularly those diagnosed with schizophrenia, for whom ‘fi rst rank’ symptoms include hallucinations, delusions or paranoid thoughts, disorganization of thoughts, or a belief that their thoughts and actions are infl uenced by or controlled by an external agent. Such symptoms are described as ‘positive symptoms’, and occur alongside ‘negative symptoms’ such as apathy, social withdrawal, lack of motivation or poor concentration.