This book explains, from a public law perspective, the constitutional purpose and significance of audit, a topic which has been largely neglected, and casts light on important aspects of accountability in the British system of government. The book suggests that audit, as an accountability mechanism, has been underplayed to date and that greater significance should be attributed to its role in delivering both democratic accountability and, within government, managerial accountability. The focus of the book is central government audit in Britain, but the constitutional role of audit at a local level and at a European Union level is also considered. The book begins by explaining, in a non -technical way, the basic concepts of accounting and audit, and sets audit in its historical context. The different types of audit and the institutional framework within which audit is conducted are then analysed. Any shortcomings in each area are identified and suggestions for change are explored. The constitutional significance of the changes to the role of audit that are currently taking place are analysed, as are the effects of developments, such as the creation of agencies, contracting-out, and more recently, resource accounting and budgeting and devolution, on the constitutional role of audit. The fundamental principles, both institutional and substantive, of public sector audit are identified and new tasks that audit could fulfil at central government level are proposed.