Glioblastoma, a highly lethal brain tumor, features extensive heterogeneity at the cellular and molecular levels. The discovery of glioma stem cells (GSCs) supports a new paradigm in tumor biology and therapeutic targeting. GSCs contribute to the cellular origin of primary gliomas and the recurrence of malignant gliomas after traditional treatments. A growing body of evidence suggests that GSCs, just as the bulk tumor cells, are heterogeneous with phenotypic and genetic complexity. Heterogeneous GSCs may add to glioblastoma heterogeneity and impact response to current therapies. A better understanding of GSC heterogeneity is required to facilitate the design of more effective therapies against this highly malignant brain tumor. © 2014 Bentham Science Publishers.