Recent years have witnessed a vibrant debate concerning the constitutional basis of judicial review, which reflects a broader discourse about the role of the courts, and their relationship with the other institutions of government, within the constitutional order. This book comprehensively analyses the foundations of judicial review. It subjects the traditional justification, based on the doctrine of ultra vires, to criticial scrutiny and fundamental reformulation, and it addresses the theoretical challenges posed by the impact of the Human Rights Act 1998 on administrative law and by the extension of judicial review to prerogative and non-statutory powers. It also explores the relationship between the theoretical basis of administrative law and its practical capacity to safeguard individuals against maladministration. The book seeks to develop a constitutional rationale for judicial review which founds its legitimacy in core principles such as the rule of law, the separation of powers and the sovereignty of Parliament. It presents a detailed analysis of the interface between constitutional and administrative law, and will be of interest to all public lawyers.