The article studies how judicial practice is influenced by evaluation concepts and how disputes should be resolved when reasonableness comes into collision with standards of positive law. From 1994 to 2015 the Constitutional Court of the Russian Federation used the concept of reasonableness in one of thirteen decisions (1655 out of 23127), the Supreme Court of the Russian Federation uses this concept in approximately one of twenty cases (93,197 out of 4,501), the Supreme Arbitration Court of the Russian Federation — in one of fifty-three decisions (5,688 out of 306,068). One in four decisions of the European Court of Human Rights concerning the Russian Federation in 2014 deals with the provision of reasonableness (46 out of 209). Actually, there are many unsolved problems determined, in particular, by the conditions and limits of the concept of reasonableness interpretation. These problems are caused by lack of conceptual framework of the subject, as well as serious division of scholars’ opinions on many issues. The lack of theoretical studies of the research topic, the diversity of contentious issues in the application and interpretation of the concept makes the topic of this article important. In-depth study of the forms of implicating reasonableness in legal practice may contribute to the development of Russian legal science.