In our current-day world of corporate scandals, financial crises and demands for better corporate governance, the role of the IAF has become more and more important. As a result, external and internal stakeholders such as investors, regulators, and corporate boards increasingly focus on the IAF, in particular on the relationship between internal and external auditors (Gramling et al., 2004a; Glover et al., 2010; Schneider, 2009; Munro and Stewart, 2011). In this evolving environment, EAs are facing several challenges, like extended audit requirements and audit fee pressures for instance (Abbott et al., 2010). One way to combat these challenges would be to work towards an effective and efficient integration of the internal and external audit functions. Especially, since professional auditing standards (e.g., ISA 610) permit EAs to rely on the IAF. From a research perspective, Bame-Aldred et al. (2013) describe the areas of research that focus on the reliance of EAs on the IAF as very complex, since the collaboration and interactions between both functions are manifold. However, although prior research has examined a number of issues related to this reliance, several topics are unexplored. In particular, there is no empirical evidence on which determinants explicitly drive the extent to which EAs rely on the IAF. Extending prior research, this study does not only theoretically or behaviorally examine which attributes encourage the reliance of the EA on the IAF, rather it explicitly empirically investigates determinants likely to be associated with the extent of the reliance decision. With this approach we introduce a new category of IAF indicators, namely specific purposes the IAF has in the company. We explore the extent to which the EA relies on the IAF first from a CAE perspective and validate our results using additional data from EAs. Using data from a survey conducted by the Austrian, German and Swiss national Institutes for Internal Audit (IIA), we are able to explore from a CAE perspective whether specific purposes of the IAF drive the extent to which the EA relies on the IAF. In order to get insights from an EA perspective, we conduct a survey with EAs from a large audit firm in Germany.