The aim of this thesis is to provide insights into processes associated with operation of audit committees (ACs) and their effects on aspects of corporate governance. The thesis provides a critique of extant studies of ACs, develops an alternative framework for researching ACs, analyses evidence of AC operation and their effects on internal control and risk management, financial reporting and external audit in three case companies. The thesis seeks to contribute to the literature on ACs in a number of ways. First, it provides a historical background to the development of ACs (chapter 2) and examines the available international evidence relating to corporate governance effects of ACs (chapter 3). It concludes that in many areas where ACs have been expected to bring governance benefits the findings thus far are either inconclusive or very limited. Chapter 3 of the thesis also concludes that the limited contribution of the extant literature on ACs may be attributable to (i) a narrow focus on the use of the agency theory perspective, (ii) the predominant reliance on quantitative methods and (iii) the development of research around theories of AC existence rather than theories of AC operation and effects. Second, the thesis seeks to make a contribution to the literature by developing an alternative framework for conceptualising the operation and effects of ACs. The theoretical framework developed in chapters 5 and 6 draw upon institutional and power perspectives and aims to reflect better the reality of the context in which ACs operate in practice. Considering the lack of attention given to the operational and institutional context of ACs in extant studies this framework is an important contribution. Third, the thesis provides empirical evidence on the operation and effects of ACs in three companies. The theoretical framework is used to analyse the three cases individually (chapters 7-9) and for cross-case analysis (chapter 10). The investigation into AC processes and effects concludes (chapter 11) that ACs are adopted for a variety of reasons and that AC related outcomes are determined by the nature of the AC process rather than their formal terms of reference and scheduled meetings. This process is influenced by power relationships in which alliances and networks between agencies (both individual and committees/functional units) and the utilisation of standing conditions by agencies are important factors.