In contrast to many other types of cancer, epithelial ovarian cancers often exhibit differentiation patterns that are more specialized than those of the tissue of origin. Many epithelial ovarian cancers assume morphologic features reminiscent of the müllerian duct-derived epithelia, but are thought to arise from cells of the simple ovarian surface epithelium that is not of müllerian duct origin. This article discusses recent studies that implicate aberrant activation of embryonic pathways in ovarian cancer histogenesis, and highlights the intimate relationship between developmental plasticity and neoplasia.