Gliomas are the most common intracranial malignant tumors in humans, and high-grade gliomas in particular pose a unique challenge due to their propensity for proliferation and tissue invasion. Our understanding of glioma oncogenesis, proliferation, and invasion has been greatly advanced in the past 10 years as researchers have gained a better understanding of the molecular biology of these tumors. This article highlights glioma histopathology, as well as cytogenetic and molecular alterations associated with the pathogenesis of human gliomas. It is hoped that better understanding of the molecular pathogenesis of gliomas will improve tumor classification as well as lead to novel targets for therapy and prognostic markers.