A new paradigm for the pathogenesis of female pelvic cancer helps explain persistent problems in describing the development and diverse morphology of these neoplasms. This paradigm incorporates recent advances in the molecular pathogenesis of epithelial ovarian cancer (EOC) with new insights into the origin of these tumors. Correlated clinicopathologic and molecular genetic studies gave rise to a dualistic model that divides the various histologic types of EOCs into two broad categories designated type I and type II. Because serous carcinomas are the most common EOC and account for the vast majority of deaths, they form the subject of this review. Recent studies indicate that the precursor of ovarian high-grade serous carcinoma appears to develop from an occult intraepithelial carcinoma in the fimbria of the fallopian tube and involves the ovary secondarily. Another possible mechanism is implantation of normal fimbrial epithelium on the denuded ovarian surface at the site of rupture when ovulation occurs, causing the development of cortical inclusion cysts. The dualistic model serves as a framework for the study of ovarian cancer and can help investigators organize this complex group of neoplasms. It also facilitates the development of novel approaches to prevention, screening, and treatment of this devastating disease.