This paper contributes to the understanding of how external auditors rely on the work of internal auditors by analyzing the applicable professional standards and research findings. The decision aids resulting from these analyses should assist external auditors with their evaluations of internal audit staffs and reliance on their work performance. Corporate management who wish to reduce external audit costs by maximizing external auditor reliance on internal auditing should also benefit from these analyses and decision aids by knowing how to strengthen their internal audit function.