Ovarian cancer represents the most lethal gynecologic malignancy, primarily due to a lack of early detection, which results in most patients being diagnosed at an advanced stage of disease. Though the ovarian surface epithelium is thought to provide the primary site of tumorigenesis, the exact etiology of the various tumor types associated with this disease remain undefined. Recent evidence suggests that ovarian tumors, like other solid tumors, contain distinct populations of cells that are responsible for tumor initiation, maintenance and growth. These specialized cells, termed cancer stem cells, display some of the hallmarks of normal stem cells and are thought to evade current chemotherapeutic strategies, resulting in an increased risk of recurrence. Here we review evidence for the existence of cancer stem cells in ovarian malignancies and their contribution to the pathology of this disease, critically evaluate the methods used for ovarian cancer stem cell definition and isolation, and discuss their clinical relevance.