Judicial review of administrative decisions enforces a set of legal norms that confine the scope of administrative powers and constrain their exercise. One way of organising these legal norms is to divide them into three broad categories: norms concerning procedural steps such as hearings, norms concerning the reasoning process that leads to the decision, and norms concerning the content and substance of the decision itself (Cane 2011, 140, 180). This chapter surveys the comparative administrative law literature on the second of these categories: legal norms governing administrative reasoning processes. In doctrinal terms, a more common designation of judicially enforced norms confining and constraining administrative power is as grounds of review, standards of review, or simply principles governing the administration. The jurisdictions surveyed in this chapter all categorise their grounds, standards or principles in different ways. One of the advantages of the categories adopted here is that they facilitate comparison between jurisdictions. Scrutiny of reasoning processes is used in reviewing exercises of discretion. This can be understood as an answer to the tension between respecting discretion and upholding the rule of law (Mashaw 2017). Administrative discretion means a measure of decisional autonomy for administrative decisionmakers. It is necessary if the modern administrative state is to serve effectively the public interest objectives entrusted to it; and the fact that the legislature has chosen to confer discretion is a further good reason for the courts to respect it. In all of the systems surveyed, judicial review is a supervisory power that does not extend to courts substituting their own judgment for the administration’s exercise of discretion. On the other hand, however, to treat discretion as unfettered and as a lawless void would be inconsistent with courts’ responsibility to uphold the rule of law by scrutinising the exercise of public powers. The problem, then, is to identify an acceptable basis for controlling the exercise of discretion. Scrutiny of reasoning processes is the answer. Such scrutiny serves to structure the exercise of discretionary power rather than to confine its scope (Cane 2011, 172): reasoning process flaws render a decision unlawful even though it was within the scope of the power. Such scrutiny therefore both respects and controls discretion. However, the underlying tension remains, and renders the law in this area inherently unstable. That seems a likely explanation for the range of different approaches to reasoning processes that will be seen in this survey. The comparative method I adopt in this chapter is to survey the administrative law literature on a range of jurisdictions, from the perspective of three jurisdictions whose law is similar on this topic: England and Wales, Australia, and New Zealand (for simplicity, I will refer to these three as the English law jurisdictions). The narrow focus on one single category of ground or legal norm makes it possible to consider a fairly broad range of jurisdictions. The chapter deals in the greatest depth with Canada and the United States, along with the three English law jurisdictions, but it further touches on South Africa, Germany, France, and China. These jurisdictions were chosen as representative of some of the major groupings (eg civil and common law, using specialist administrative courts and general courts, Eastern and Western, liberal and authoritarian, different governmental structures), and because an adequate volume of literature in English exists for them. None of the comparator jurisdictions is treated in any comprehensive fashion. Instead, each is mentioned only for one or more features of its law on reasoning processes that differs from the English law jurisdictions in an interesting way. The purpose of this type of comparison is illumination rather than the riskier purpose of promoting transplantation or harmonisation: considering the range of approaches to scrutiny of reasoning processes casts light on the role and function of these controls, and on the significance of our own jurisdiction’s doctrinal solutions. I have found this exercise very enlightening, particularly in highlighting different distinct modes of ensuring some respect for administrative discretion. Yet there is a great dearth of comparative sources on review of reasoning processes: virtually no studies are devoted specifically to this topic, and treatments of the topic in broader studies are often very brief. One of my main messages, therefore, is that there is much scope for in-depth comparative research on this topic. This chapter briefly outlines the law on reasoning processes in the English law jurisdictions; traces some divergences in the details of the law among these three, and with other jurisdictions that share a similar approach; and then considers jurisdictions with significantly different approaches. The latter are where there is no review of reasoning processes; where scrutiny of reasoning processes is available on a much broader basis; where there are possibly different approaches to the standard of review; and where there has been a shift away from review of reasoning processes to assessment of outcomes. Towards the end, there is brief consideration of possible correlations with system types, and the chapter concludes with some reflections.