The term glioblastoma refers to a variety of different diseases, and there is no clear cause for these. Some glioblastomas are caused by copy number alterations or defining genetic mutations, typically involving just the tumor cells themselves. While there are some heritable conditions that predispose to the development of glioblastomas and other brain tumors, the overwhelming majority of glioblastomas occur sporadically, meaning that there is no familial or genetic risk. Glioblastoma appears to occur slightly more frequently in Caucasian ethnicities, although our understanding of ethnic contributions to glioblastoma is definitely incomplete. The contribution of environmental factors has been studied and the only likely candidate has been exposure to high dose ionizing radiation. Factors such as head trauma, diet, radio-frequency or electromagnetic radiation have really shown very little suggestion of a link.