Ovarian carcinomas are a heterogeneous group of neoplasms. Pathologists currently employ a morphology-based classification system to divide ovarian carcinomas into major subgroups based on degree (tumor grade) and type of differentiation (eg, serous, endometrioid, clear cell, or mucinous). Molecular studies have shown that specific genetic defects are likely to be present in certain histologic types of ovarian carcinomas and unlikely to be present in others. Within the serous and endometrioid carcinomas, the molecular defects in low-grade versus high-grade tumors also appear to be largely distinct. Recently, mouse models of ovarian carcinoma have been developed that recapitulate many of the morphologic features and biologic behavior of selected subtypes of ovarian cancer. It is expected that these mouse models will yield new insights into ovarian cancer pathogenesis and prove useful for preclinical testing of novel strategies for ovarian cancer treatment.