Comity is the duty of one authority to respect and to support the proper function of other authorities. This book is mostly about comity among public authorities. I aim to explain how administrative law can enable them to work together to give effect to the constitutional principles that support responsible government. I hope that the focus on constitutional principles will help to bring some order to the very diverse topics with which you need to deal, if you are to understand this incredibly complex branch of public law. Public law imposes duties to serve the public interest. It governs all of us (criminal law and the law of tax and of child protection are parts of public law). Administrative law is the public law of administration. It is the body of legal standards that establishes executive institutions of government, and confers governmental powers and imposes duties on public authorities. It creates frameworks that govern social security, public education, planning, competition, employment, local government, the National Health Service, immigration and asylum, the police, prisons, probation, ASBOs, the armed forces, the ministers of the Crown, and every department of government.