Abstract: The object of this research is the practical principles of rational-emotional-behavioral therapy (REBT) by A. Ellis. The subject of the research is the specifics of the formation of the conceptualization of the client within the framework of a rational-emotional-behavioral approach. The aim of this research is to develop an algorithm for compiling client conceptualization in the therapeutic direction under consideration based on the systematization of activating events, irrational beliefs, key contesting counterarguments and rational statements. The conceptualization developed in this research also allows the client to form abstract ideas about problematic areas of life, to discover common cognitive behavioral patterns ("schemes") peculiar to him, to derive abstract irrational beliefs and rational statements (a new effective philosophy) and behaviorally reinforce the latter in order to realize significant (including global) life goals and values. The methodological basis of the work is the research of the founders and representatives of rational-emotional-behavioral and cognitive psychotherapy. The main result of the conducted research is the developed REBT conceptualization, which until now was absent in rational-emotional-behavioral therapy, but is actively used in a related psychotherapeutic approach – A. Beck's cognitive therapy. The presented conceptualization and the described algorithm of its compilation contribute to eliminating the risks associated with an insufficiently systematic understanding by the client of the abstract structure of his emotional and behavioral disorders during the passage of rational-emotional-behavioral therapy, known for its deep philosophical approach to solving specific problems, mainly due to philosophical disputation of specific irrational beliefs of the client. The scientific novelty of the work also lies in the description of cognitive-behavioral patterns ("schemes") characteristic of the majority of clients suffering from affective disorders, formulated on the basis of twelve typical irrational beliefs identified by A. Ellis in 1956.