The Legal Nature of the Review of Antimonopoly Authority Decisions Based on New or Newly Discovered Circumstances: Existing and Appropriate Guarantees of the Legality and Certainty of the Administrative Procedure Russian legislation, judicial practices, and enforcement practices of antimonopoly authorities reveal uncertainty regarding the administrative procedure for reviewing antimonopoly authority decisions based on new or newly discovered circumstances. There are discrepancies regarding the commencement of administrative liability periods for violating antimonopoly legislation, and entrepreneurs' rights to transparency and certainty in administrative procedures. The questions raised have both theoretical and practical significance, and their discussion has the potential to improve and harmonize Russian antimonopoly and administrative legislation.