Abstract: The article analyzes the functioning of information systems using systemic and synergistic approaches. The latter is caused by the conditions of uncertainty, chaos of deep social transformations and cyberwars in the modern information space. The latest scientific intelligence in the field of information security methodology and the place of a synergistic approach in it have been highlighted. The main methodological principles of synergetics as an interdisciplinary scientific area have been considered: self­organization, bifurcation, fluctuation, nonlinearity, dissipation, attractors. Synergistic effects have been highlighted as interdisciplinary formations which explain the formation and selforganization of models and structures in open systems. The synergistic effects inherent in information systems as a complex system entity have been studied. The information security system has been considered as a complete, multifunctional, dynamic, open structure with its inherent features. It has been proven that traditional views on the study of the functioning of such systems are currently ineffective, as they are characterized by constant stochasticity and variability. As an alternative to classical methods, it has been proposed to use the phenomenon of information entropy in the study of such systems. Modeling of the information security process taking into account the entropy of the system has been suggested. It is worth noting that the information security system is a subsystem of the national security of Ukraine in general, therefore, the analysis of its functioning in the modern conditions of the war against Russian agression and constant cyber threats of the enemy acquires strategic importance