The distinctive domain and character of public law have become—and in certain respects always were—unclear and, to a degree, contested. As a result, any definition is likely to be to some extent stipulative. For my purposes, I want to refer to public law in two broad and related senses—as applying to a certain kind of body and its functions, and as requiring a certain kind of justification. The first sense refers to the actions of the state and its administration. Of course, it will be pointed out that these are increasingly performed by private bodies and often involve legal activities that have been associated with private parties and doctrines, such as procurement and contract. Nevertheless, government and the administrative apparatus more generally can still be considered as possessing distinctively broad, authoritative, and coercive powers which in various ways make their subjection to the law both problematic and pressing: Problematic in that they play a central role in the making and enforcement of the law, pressing in that this role renders them more powerful than other bodies. The second sense enters here. For the justification of state power has come to rest on its serving the public ends of the ruled rather than private ends of the rulers, and certain public qualities of law have been thought to oblige those who wield state power to do so in a publically justified and justifiable way. Ruling through laws has been viewed as different from rule by willful, ad hoc commands because laws have certain characteristics that render them capable of coordinating and shaping public behavior in consistent and coherent ways over time, while ruling under the law likewise forces rulers to adopt public processes and offers an additional incentive to devise laws that treat rulers and ruled equitably. Again, these matters are far from straightforward. How far laws need to, or even can, always possess the requisite qualities and the degree to which these do constrain power holders are matters of dispute. Yet, that all law has to have some public qualities—for example, that it be promulgated and capable of being followed in ways that make it publicly recognized as law—and that these features formalize power to a degree, is reasonably undisputed. Increasingly, though, and even more controversially, many jurists have wanted to suggest that legality also involves certain substantive qualities of a public kind—that laws must appeal to public reasons that all subject to them can accept as reflecting, or being compatible with certain basic interests or values that are equally shared by all. Such arguments have come to be identified with rights and in particular constitutional rights, which are deemed to set the terms of how and to what purpose political power may be legally exercised. In this way, the two senses of public law come together. Constitutional rights define and mark the limits of public power in ways that can be publicly justified, and thereby ensure it serves public ends. They thereby serve what Martin Loughlin calls the “basic tasks of public law;” namely, “the constitution, maintenance and regulation of governmental authority.”