Tumor cell growth and invasion within the CNS imply complex interactions among malignant cells, neural cells, and endothelial cells. Various in vitro assays have been developed to study tumor cell invasion that includes the use of cocultures between tumor spheroids and organotypic cultures of normal brain tissue. Furthermore, various animal models have been developed to study biologic characteristics of brain tumors. At present, there is evidence that several growth factors are involved in both endothelial and tumor cell proliferation, whereas the interrelationship between glioma growth and invasion is less well established. It is also emerging that the process of invasion is characterized by dynamic interactions between the extracellular matrix, proteases, and specific cell surface receptors. The dissemination of tumor cells within the CNS also involves a passive component where single tumor cells may follow specific pathways mediated by the constant flow of cerebrospinal fluid.