Cognitive flexibility is considered as a person’s mental ability to organize one’s own cognitive activity and intellectual behavior in response to changing environmental conditions. Though the construct of cognitive flexibility has been well investigated in different contexts of its manifestation, yet there is no general operational definition of this construct in cognitive studies. This study aimed to explore the current theoretical views on the problem of a person’s cognitive flexibility and to indicate the contribution of these views to the development of the measures of cognitive flexibility within the psychological treatment. In brief review of Russian and foreign cognitive studies, the ideas about the term “cognitive flexibility” has been summarized as a mental ability of a person, a skill to change cognitive attitudes in response to the changing conditions of one’s own life. It was shown that there has been a lack of definitions in Russian to describe the phenomenon of cognitive flexibility, and it has not been studied in terms of content and forms of its manifestation in human behavior, especially, in intellectual behavior. In foreign cognitive studies the term cognitive flexibility is widespread. It is referred to in studies of cognitive abilities and skills. The majority of researchers determine its operational definition as a general property of personality’s cognitive system. At the same time, it is not known what this property is. For the purposes of the present study, the approach to examine the person’s flexibility has been put forward. It was considered as a specific ability of cognitive system and a property of different cognitive processes. This approach uses abilities as the properties of functional system, which bring about specific mental functions. In reviewing the existing measures of cognitive flexibility, it was demonstrated that the lack of operational definition of this construct usually leads to the choice of the instrument in accordance to aims and goals of the research. Cognitive tests and self-report measures were considered as two main instruments in examining person’s flexibility. Their applicability was proved and it was shown that the instruments examine the type of cognitive flexibility needed for change to adaptive behavior within psychological treatment.