Cancer is the second leading cause of morbidity and mortality worldwide, ranking just after cardiovascular diseases. In the central nervous system, gliomas constitute the most frequent type of tumors. According to the definition, oligodendrogliomas are diffusely infiltrating glial tumors, composed of neoplastic oligodendroglial cells, typically found in cerebral hemispheres in adult population, although not uncommon in children. They encompass a range of tumours, from well-differentiated to frankly malignant neoplasms. In the current World Health Organization (WHO) classification of tumors of the central nervous system, covering a four-tiered WHO grading scheme, oligodendrogliomas are recognised as grade WHO II and WHO III by the degree of malignancy. They may be either well differentiated, composed of neoplastic cells that morphologically resemble oligodendroglia, or may harbor focal or diffuse features of malignancy, respectively. Their prognosis is in this case less favorable. This book provides current research on the diagnosis, outcomes and prognosis of oligodendrogliomas. Chapter one examines the pathology, molecular mechanisms and clinical references of ODs. Chapter two discusses the ODs and the problematic diagnostic markers. Chapter three examines the histopathologic features of oligodendrogliomas and of an assortment of other central nervous system neoplasms that can resemble them and reviews features that allow one to sort through these histopathologic differential diagnoses. The final chapter reviews speech mapping in oligodendroglioma operations and provides data regarding patient outcomes with these methods.