While the effect of auditor industry specialization is well documented in prior literature, it is unclear under what conditions or for which type of firms an auditor's industry expertise matters. I hypothesize that industry specialist auditors will provide higher quality audits in settings where the likelihood of revenue manipulation is greater. I use a firm's manipulation of revenues to measure audit quality because the revenue account is significant, requires in-depth industry specific knowledge, and is subject to frequent manipulation. The results suggest that the impact of industry specialists is concentrated among firms with complex revenue recognition standards, high growth, and low institutional monitoring. Overall, my findings highlight the importance for regulators, auditors, clients, and investors to consider the circumstances in which industry expertise improves the quality of an audit.