The source material of the book is translated from the only existent Sasanian law text and two Rivâyats from the first half of the ninth and the first half of the tenth century, at which time the Zoroastrians survived only in minority communities. The original text is presented in photocopy with a transcription. The analysis is concerned with four institutions in the sphere of family law: Guardianship, marriage of levirate, marriage of a woman in order to provide her father or brother with an heir and marriage between close relatives (incest taboo did not exist). The issue of the research is to show how the social conditions and internal family economy with its power balance is reflected in the rules of the Sasanian law, and that the differences apparent in the later texts are not accidental, but form a pattern caused by the changing social conditions, and that the law was changed in order to help preserve the Zoroastrian minority in adversity under Arab rule.