This chapter describes the classical subtypes, differential diagnosis, epidemiology and genetics of schizophrenia and related disorders. Relatives are examined for some of the biological abnormalities which are found in their schizophrenic kin. The relatives of patients with schizophrenia have also been reported to be more likely than control subjects to have poor performance on cognitive tests measuring memory functions. The discovery of risk factors acting in early life has been central to the neurodevelopmental hypothesis of schizophrenia. Magnetic resonance imaging (MRI) studies have consistently demonstrated that people with schizophrenia have increased lateral ventricular volume and also show a slight decrease in cortical volume with greater decrements in the hippocampus, amygdala and thalamus. Children destined to develop schizophrenia often have subtle developmental delays and deficits in motor and cognitive function, tend to be solitary and show an excess of social anxiety. The chapter reviews the essential principles of management for psychosis.