Book excerpt: For both ancient Egypt and Iran, as a cultural feature, incestuous relationships are usually dismissed on the grounds that they are only found as the exception, being allowed for royalty as representatives for the divine on earth, or that the evidence for such relationships are unreliable. Neither view, from the perspective of this study, is tenable. This work examines the evidence for marriage and sexual relations between siblings, and between a parent and child, in ancient Egypt and pre-Islamic Iran. The book restricts its examination to incestuous relationships between members of non-royal nuclear families and puts forth arguments against the generally held axiom that the prohibition of incest is a universal phenomenon.