The cancer stem cell theory postulates that tumors are sustained by a select cell population with specific features, such as self-renewal ability and the capacity to give rise to a heterogeneous mass of tumor cells. The existence of such cells has been demonstrated for glioblastoma, with these cells being referred to as glioma stem cells (GSCs). Glioblastomas are notoriously heterogeneous tumors, however, and the isolation and characterization of their stem cells will require further investigations. Furthermore, the lack of unequivocal markers for GSCs and a partial overlap in characteristics with other cells often lead to confusion. Here, we review the characteristics necessary for a glioma cell to be considered a stem cell, and we adopt our murine glioblastoma model based on genetically modified neural stem cells to illustrate and discuss the GSC concept.