The legitimation of administrative discretion is closely linked to empowering courts to review discretionary administrative acts. At the same time, a system of criteria designed to enable such review emerged. This article examines the key and several supplementary criteria used by courts to assess administrative discretion, demonstrates methods of their legal formalisation, and draws conclusions regarding the most appropriate and effective methods. The primary methodology employed is comparative legal analysis. This approach makes it possible to examine the models for legal formalization of these criteria in Austria, Germany, France, and several Central Asian countries, and to compare them with Russian judicial practice and legislation. The Author concludes that administrative discretion should not be institutionalised as a separate institution of administrative law, as doing so risks eroding its essential characteristics and diminishing the effectiveness of public administration. In all countries studied, discretion enters administrative law through criteria that limit it and thereby enable courts to review the legality of discretionary administrative acts. The main criteria are the lawful purpose and scope of powers of administrative bodies, while additional criteria consist of general principles of administrative law (administrative procedure). These principles have been developed by courts and scholarly schools and are closely tied to constitutional provisions. Therefore, there is no need for their codification; statutory definitions would merely restate well-known principles and would not add anything substantively new. Codification is justified only when a principle is absent from the legal system and the legislator is introducing it for the first time. Importantly, even once a principle has been codified, it will still require judicial interpretation; courts will continue to refine its meaning and methods of application. In Russia, the main principles, including proportionality and the protection of legitimate expectations, have long been recognised by courts and doctrine. They are affirmed in the decisions of the Constitutional Court, which the Supreme Court follows. Nonetheless, the Russian legislator continues to codify them in various statutes, including legislation on state control. The Author concludes that the Supreme Court should apply these principles more actively when reviewing administrative discretion. In particular, the protection of legitimate expectations requires greater attention from the Plenum of the Supreme Court.