Schizophrenia is a disorder that begins at a young age and causes severe mortality and morbidity. The aetiology and pathophysiology of schizophrenia are still not known precisely. It is a very complex syndrome, and it is thought that more than one aetiological factor plays a role in its emergence. Genetics, epigenetics, and environmental and gene-environment interaction play a role in the aetiology of the disease. In addition, post-mortem neuropathological findings, neuroimaging findings, neurochemical studies, neuropsychological study results, and neurophysiological study results shed light on the mechanisms that cause the disease to occur. This chapter will provide an overview of the diathesis-stress, neurodegeneration, and neurodevelopmental models and summarise the work done so far in many areas.