The classification of epithelial ovarian cancer has been substantially revised, with an increased appreciation of the cellular origins and molecular aberrations of the different histotypes. Distinct patterns of signaling-pathway disruption are seen between and within histotypes. Large-scale genomic studies of high-grade serous cancer, the most common histotype, have identified novel molecular subtypes that are associated with distinct biology and clinical outcome. High-grade serous cancers are characterized by few driver point mutations but abundant DNA copy number aberrations. Inactivation of genes associated with DNA damage repair underlies responses to platinum and PARP inhibitors. Here we review these recent developments. Cancer Res; 72(11); 2701–4. ©2012 AACR.