The study of ovarian embryogenesis can provide important clues about the etiology and development of the different subtypes of ovarian neoplasms. The coelomic epithelium, also called germinal epithelium, was once thought to represent the site of origin of most cellular elements present in the adult ovary. However, recent observations at the morphological, functional, and molecular biological levels strongly suggest that this epithelium plays little or no role in ovarian development. The same observations provide strong support for an important role of the components of the fetal excretory system. These conclusions weaken the hypothesis that the coelomic epithelium is the site of origin of ovarian epithelial tumors. Knowledge of the origin and maturation of germ cells can shed light on several clinico-pathological characteristics of germ cells tumors, including their occasional extra-gonadal origin and differences in the biological behavior of ovarian versus testicular lesions. Knowledge of the mechanisms of regulation of mitotic and meiotic activity during ovarian germ cell maturation can provide insights into the molecular genetic determinants of germ cell neoplasms. The elucidation of molecular pathways actively involved in controlling gonadal differentiation may shed further light into our understanding of the relationship between aberrant differentiation and predisposition to gonadal cancers.