This thesis seeks to provide a comprehensive overview of the extent and use of public inquiries appointed by the Commonwealth government since federation. Given the increased incidence in public inquiries since the 1970s, particular attention is given to assessing inquiries during this period. The thesis develops a clear definition of public inquiries to better identify the number established and to distinguish them from other advisory institutions and to allow more accurate comparison of their use by different governments over extended timeframes. The thesis addresses a number of key issues concerning public inquiries such as the reasons for their appointment, their roles and functions in the political system, their powers of investigation, processes of operation, their different organisational forms and their impact on policy development. In addition, the thesis seeks to explain both the long term use of public inquiries in Australia, and in particular their increased incidence since the 1970s. Supported by new data, and a more rigorous definition of public inquiries, the thesis identifies trends in the number and type of public inquiries appointed, their use by different governments, the range of issues investigated, the processes employed and the changing composition of their memberships. The thesis proposes that an important means of explaining the continuing appointment of inquiries is their intrinsic 'publicness' - their public appointment, external membership, temporary nature, open processes, and public reporting arrangements. This 'publicness' has given public inquiries a particular standing and legitimacy in the political system that for a variety of reasons, other institutions are increasingly unable to provide. Other issues concerning public inquiry appointment such as the effect of government partisanship, the impact of the electoral cycle, and the political motivations of governments are also assessed. A number of theories such as public choice are examined in relation to explaining inquiry appointment and found to have limited application in providing an overall explanation of inquiry use and their functions. These different issues are analysed by examination of many individual inquiries and supplemented by in depth assessment of three clusters of case studies. The case studies cover seven inquiries of different types and powers appointed over a twenty year period by both Labor and Coalition governments into a range of different fields including public sector reform, allegations of corruption and maladministration and financial deregulation. Each set of case studies examines why the inquiries were appointed, their classification and type, the processes employed, the form and content of their reports, and their policy impact. The thesis concludes that in examining why public inquiries are appointed and their roles in the political system, they need to be assessed not just by the effectiveness of their processes or the quality of their advice. These are important, but alone are not sufficient in explaining the persistent use of inquiries by all governments and their proliferation since the 1970s. The thesis contends that it is the 'publicness' of inquiries which distinguishes them from other advisory bodies and gives inquiries particular standing in the Australian political system to be perceived to be able to legitimately investigate and advise on a wide of issues. Despite the growth of other advisory bodies in recent times, public inquiries have continued to be appointed in increasing numbers since the early 1970s regardless of the government in power and therefore need to be seen less as an aberration of the Australian political system and more as an important, if often understudied, component. Future research areas recommended include the need for greater comparative analysis of their use with other Westminster democracies such as the United Kingdom, Canada and New Zealand.