This thesis presents empirical research on the perceptions of external auditors (EAs) regarding the impact of three dimensions of auditing, namely the objectivity of the Internal Audit Function (IAF), the competence of the IAF, and the work performance of the IAF, on (1) the effectiveness of the IAF in Jordanian companies listed on the Amman Stock Exchange (ASE) and (2) EAs’ decisions to rely on the work of internal auditors (IAs). In addition, this thesis investigates Jordanian EAs’ level of self-insight into the importance of the three dimensions when (1) evaluating the effectiveness of the IAF and (2) deciding on the degree of reliance on IAs