Chapter 5 argues that there is a distinctive activity and with it a particular problem, a particular kind of mischief, that is the central concern of the rule of law ideal. The activity is the exercise of power. The focus is not on the purpose of power’s exercise, for which we have other concepts, but the way it is exercised. The goal is to minimise arbitrary ways of exercising it. The chapter explicates the notions of power and arbitrariness. It argues that power itself is not an evil but a necessity for many good things. Nor for that matter is arbitrariness evil in itself. Rather, it is the combination of arbitrariness with power, when substantial, that is obnoxious. It suggests several reasons why it is both intrinsically immoral and likely to have bad consequences. The chapter concludes by arguing that hostility to arbitrary power is rarely the only game in town, but it is almost always justified. Power that is not arbitrary is not what we most want out of life, but it is a condition for many of the things we do want. Hostility to it is immanent in the rule of law ideal.