ABSTRACT With the growing relevance of internal auditing, academics and practitioners emphasize the importance of an adequate and adaptable staffing approach. Because internal audit resources are considered a crucial component of internal audit quality, we investigate why internal auditors perform audits with experts from within or outside the organization. These joint audits augment resources and represent a viable alternative to additional staffing or full outsourcing of the internal audit function (IAF). Using survey data from three national chapters of the Institute of Internal Auditors (IIA), we consider three IAF dimensions (i.e., structure and resources, activities and processes, environmental factors) associated with resource augmentations. Our findings provide evidence that joint audits are used when the IAF is comparatively small and competent, when the IAF focuses on risk and strategy-related tasks, and when the IAF is decentralized. Our findings also suggest that joint audits can strengthen the auditor-auditee relationship. Data Availability: Please contact the authors. JEL Classifications: M42; M49.