Malignant glial tumours are the most common primary brain tumours and the most aggressive and difficult to treat. Gliomas present heterogeneity histologically, genetically and in their outcome. Despite decades of intense research in this field, there has been little improvement in mortality rates because of the tumours’ inter- and intra-tumoural heterogeneity and predisposition of the cancerous cells to infiltraate normal parenchyma of the brain. Gliomas have been traditionally categorized based on their histopathological features, but it has become obvious that this classification alone has its limitations. Recently, expression studies have indicated that by using molecular signatures, malignant glial tumours can be categorized into subclasses that can more effectively predict patient outcome. The use of molecular markers that carry both prognostic and diagnostic information on tumours with histologically reminiscent appearance adds another level of complexity, reduces inter-observer variability, and allows better characterization of novel tumour variants and entities. In modern neuro-oncology, molecular markers have become essential in tumour evaluation, and molecular marker status of a glioma now guides clinical decision-making. This review will discuss general aspects of malignant gliomas, their grading and staging, genetic information and relevant molecular markers, as well as future perspectives in the treatment and classification of these gliomas.