Ovarian cancer, as used in this review on drug resistance, applies to the study of the problem in those malignant tumors which arise from the modified peritoneal mesothelial cells, which cover the ovarian surface. These tumors are, by far, the most common malignancies of the ovary and display a remarkable range of histological features, which generally recapitulate those of the endocervix, endometrium, or Fallopian tube to which the ovarian surface epithelium is embryologically related. Of direct relevance to the issue of chemotherapeutic responsiveness is the fact that, stage for stage, some of these tumor subtypes carry a worse prognosis. The need for chemotherapy in ovarian cancer arises because this disease produces vague symptoms that occur only after it has spread from the confines of the ovary to the surfaces of the peritoneal cavity. At this stage, surgery rarely can eliminate all apparent disease, and even in those cases, experience shows that the disease will recur with high probability. This makes it obvious that residual microscopic disease remained after surgery. Hence, the majority of ovarian cancer patients require chemotherapy and its effective use has proved a tremendous challenge as evidenced by the approximately 14,000 deaths from this disease in the United States in 1997.