The executive branch in Western democracies has been handed a virtually impossible task. Expected to ‘imperially’ direct the life of the nation through thick and thin, it is concurrently required to be subservient to legislation meted out by a sovereign parliament. Drawing on a general argument from constitutional theory that prioritizes dispersal of power over concepts of hierarchy, the book argues that the tension between the political dominance of the executive branch and its submission to law is maintained by the adoption of various forms of fuzziness, under which a guise of legality masks the absence of substantive limitation of power. Under this 'internal tension' model, the executive branch is concurrently subservient to law and dominant over it, while concepts of substantive legality are compromised. Drawing on legal and political science research, the book classifies and analyses thirteen forms of fuzziness, ranging from open-ended or semi-written constitutions to unapplied legislation. The study of this unavoidable yet problematic feature of the public sphere is addressed descriptively and normatively. Adding detailed examples from two fields of law, emergency and air-pollution law, in two systems (the UK and the US), the book ends with a call for raising the threshold of judicial review, grounded in theories of participatory and deliberative democracy. This innovative book, concerned with an area that has been surprisingly under-researched on a general level beyond extensive studies of national executives, offers a theoretical foundation that should ground all analyses of the arguably most powerful branch of modern government.