This guide reviews the clauses in AS 1821 to 1823, and attempts to explain why the element covered by a paticular clause is a desirable part of a quality control system. In appropriate cases it provides a suggested interpretation and course of action likely to satisfy the provisions of the clause. Suggestions as to the elements to be investigated, factors to be considered in the evaluation of a supplier's quality control system, and questions that should be answered as the result of an evaluation of a particular element of the supplier's system, are included for the guidance of the representative of the purchasing organization.