Laws of Ritual Purity: Zand ī Fragard ī Jud-Dēw-Dād (A Commentary on the Chapters of the Widēwdād) describes the various ways in which Zoroastrian authorities in the fifth-sixth centuries CE reinterpreted the purity laws of their community. Its redactor(s), conversant with the notions and practices of purity and impurity as developed by their predecessors, attempt(s) to determine the parameters of the various categories of pollution, the minimum measures of polluted substances, and the effect of the interaction of pollution with other substances that are important to humans. It is therefore in essence a technical legal corpus designed to provide a comprehensive picture of a central aspect of Zoroastrian ritual life: the extent of one’s liability contracting pollution and how atonement/purification can be achieved.