SYNOPSIS In large audit firms, interoffice knowledge sharing is embedded in two networks: the branch network, comprising all branch offices, and the client network, formed by similar engagements. Proximity between branch offices may enhance knowledge accessibility, whereas similarity between engagements could impact the relevance of that knowledge. I investigate how the two networks jointly influence the effectiveness of knowledge sharing. I construct client networks based on the similarity of clients’ product offerings and find that clients with greater centrality in the neighboring client network benefit more from knowledge sharing in terms of improved audit quality. I further show that this effect only exists when similar clients in neighboring offices are larger in size and is more salient when there is a gap in expertise between the current auditing office and neighboring offices. By enriching our understanding of interoffice knowledge sharing, these results offer practical insights to auditors, regulators, and audit-report users. Data Availability: Data are available from the data sources indicated in the paper. JEL Classifications: M42.