Internal audit in the Saudi public sector has been officially required since the Cabinet Decree in 2004, which stipulated the need for all organisations subject to audit by the General Audit Bureau (GAB) to establish internal audit departments. In this context, this study investigates the nature and practice of internal audit in the Saudi public sector, focusing specifically on an examination of the relationship between five factors known to influence internal audit effectiveness - namely: the competence of the internal audit department, the size of the internal audit department, the relationship between internal and external auditors, the management support for internal audit, and the independence of the internal audit department (as independent variables) - and the effectiveness of internal audit (dependent variable). A mixed research methodology was used in the study, archival, questionnaire and interview based - it being thought that this was likely to be the most effective approach in terms of obtaining and appropriately interpreting the available information. Two questionnaires were designed, the first being directed to internal auditors in the Saudi public sector covering the independent variables; the second questionnaire directed to managers in the public sector covering the dependent variable. Thirty-four (34) semi-structured interviews were conducted with 2 internal auditors, 15 senior managers in public sector organisations, 10 external auditors (working in the Saudi General Audit Bureau), 2 senior managers from Ministry of Finance and Ministry of Civil Service, and five interviews were conducted with managers in public sector organisations that, notwithstanding the Cabinet Decree, did not have an internal audit function primarily in order to explore the main factors for not establishing this function in their organisations. The analysis of the data collected offered a range of insights as to the nature and practice of internal audit in the Saudi public sector. A picture emerged of a fledgling practice and one which was not necessarily fully understood by both practitioners and wider stakeholders. A key finding was the importance of management support as the main driver in terms of ensuring the perceived effectiveness of the internal audit function. Management support was important as a construct in its own right but also via its links to issues of resourcing, competence and qualification, and independence. Beyond this there were a number of institutionally related findings of interest. These included the fact, noted above, that internal audit was not actually present in a significant number of Saudi public sector organisations albeit it being a statutory requirement. It was also noted that the underpinnings of that statutory requirement the Saudi Internal Audit Regulation (2007) did not tie in directly with perceived worldwide best practice - the International Standards for the Professional Practice of Internal Auditing (SPPIA). Significant differences both in practice and institutional set up were also identified between `pure' government organisations (ministries, government departments etc) and government companies in which the direct state influence was smaller. For example all government companies of any standing had internal audit functions and all had audit committees - whereas not all government organisations had an internal audit function and none had audit committees. Not only were there institutional differences - analysis of the interview and questionnaire data clearly revealed significant differences in the perceptions of internal audit effectiveness between the two types of entity with internal audit being seen as `better' across almost all the identified variables in government companies. The final chapter of the thesis seeks to reflect on the findings of the study within a wider milieu of the extraordinary development of a nation which seventy years ago comprised a disparate collection of tribal groups for whom economic perspectives had changed little for many centuries to a state which today has very significant economic power and influence. Here questions are raised as to the nature and process of change and the care which needs to be taken in the adoption of a model of accountability and control which has been developed in countries with a very different background and history. However whilst acknowledging this, it is still maintained that `better' internal audit would benefit both the economy and the people of Saudi Arabia and perhaps, in a small way, contribute to wider internal and external harmony.