This chapter provides detail description of Pathogenesis of tumours of the nervous system. Pathogenesis of tumors of the nervous system, molecular pathogenesis of gliomas, tumor oncogenes, the 12q amplicon including CDK4 and MDM2, tumors suppressor genes (TSG), retinoblastoma gene, genetic instability, hereditary syndromes, oncogenic viruses, effect of radiation, radio frequency radiation, chemical carcinogens, immunodeficiency status, hormonal factors and trauma are described in detail. 94 references are included at the end of the chapter to facilitate further reading.