Urgency of the research. Forming the energy policy of the national economy on the basis of the energy security concept will ensure making balanced management decisions concerning the future energy development of the country. Target setting. Both in the world and Ukrainian practices, the most common approach to forming a model of energy security is based mainly on sources of energy supply. However, such approach does not reflect the aggregation of the complexity of the relationship in energy systems. Actual scientific researches and issues analysis. Problems of studying national energy security are highlighted in works of such scientists as J. Jewell and A. Cherp, A. Kachynskyi, B. Kruyt, A. Mikhalevych, B. Sovakul, A. Shevtsov, A. Smenkovskyi, as well as of different international organizations. Uninvestigated parts of general matters defining. The concept of energy security requires further consideration in the context of a systems approach and its operationalization at the methodological level. The research objective is the conceptualization of energy security on the basis of a systems approach and its operationalization using the 4E model. The statement of basic materials. The article studies the features of functioning of energy systems and proposes a system concept of energy security. The authors suggest considering the subsystems of energy supply, energy conversion and energy consumption as its components, the assessment of energy security of which at the methodological level is performed using the corresponding system indicators: energy dependency, energy efficiency and energy conservation. The stable existence of an energy system is ensured by such a component of energy security as energy self-sufficiency. In the work, the approbation of the proposed methodological approach to the assessment of energy security in Ukraine has been carried out. Conclusions. Energy security should be considered as a system category, and its concept based on a systems approach. The operationalization of energy security is based on its assessment by means of the methodological approach using the 4E model: energy conservation, energy efficiency, and energy dependency, as well as energy self-sufficiency.