This paper deals with Piaget's concept of formal operations, formal operations researches and critics related to the concept. The first part of the work is dedicated to the formal operations concept. The main characteristics of formal operational thought and formal operations structure, as well as structure logical model are presented in that part of the work. The second part is a review of formal operational researches and it is divided in three parts: (1) problems of researches (2) characteristics of applied methodology and (3) author approaches as a specific research context. In the last part of the work the main critics of formal operations concept are presented and discussed.