Abstract
The effort of understanding human language and cognition, which distinguishes humans from other organisms and provides them with the opportunities they have on earth, dates back to ancient times. In line with this effort a theory of language and cognition, which is fairly comprehensive and has empirical support, has been developed based on a functional contextualistic view in the last century. This theory, called Relational Frame Theory (RFT), considers language as a verbal behavior and argues that the basis of human language and cognition is the behavior known as Arbitrarily Applicable Relational Responding (AARR). This behavior includes responding based on arbitrary relations independent of the non-arbitrary (physical) relations between stimuli, established by social whim and that do not make sense outside the social context in which they are located. AARR is characterized by three core properties such as mutual entailment, combinatorial mutual entailment and transformation of stimulus functions, and this behavior itself needs to be learned.
This review aims to explain RFT, a very complex theory, in a comprehensive and understandable way. The historical process that brought about RFT will be mentioned, the basic principles and concepts of it will be explained, and the contributions of this theory to the understanding of complex human behaviors and its approach to psychopathology will be discussed.

Key words: Relational frame theory, verbal behavior, language, cognition