The article examines the theoretical and legal issues of the essence of codification as a way of systematizing legislation. The article states that the integration processes of adaptation of domestic legislation to the legislation of the European Union oblige the domestic legislator to adapt the country’s legal system to the requirements for its systematization established by the European community. Attention is drawn to the fact that this process conditions the revision of ideas about the essence and approaches to the systematization of legislation, the introduction of new mechanisms of law-making technology. It is concluded that codification is of great importance in these processes. The article substantiates that codification, as a form of systematization of legislation, includes official activity on improvement and systematization of legal norms, which is carried out by subjects of such activity, authorized for this. It is noted that this process is carried out by systematizing legal norms into a single codified act. Codification of legislation includes a complex process of applying a special (codification) law-making technique. It is proven that this process involves the purposeful activity of law-making subjects, aimed at processing and ordering legal acts with the aim of their systematization and consistency with the needs of law enforcement activities, avoiding gaps, collisions and shortcomings. It is substantiated that the purpose of codification is the development and adoption of a single, logically constructed and internally structured act that regulates homogeneous social relations as completely as possible. It is concluded that codification should be considered a specific method of systematization of legislation, which combines the features of official systematization and law-making activity, and therefore codification has a «dual nature», which includes both the systematization of law and the active process of creating new regulatory and legal acts. It is justified that this type of activity is aimed at the radical revision and streamlining of the existing legislation, leading to the adoption of a single, fundamental and internally and externally agreed comprehensive legal act, this act regulates the most principled and fundamental social relations. It is emphasized that, from this point of view, codification should be considered as a way of systematizing legislation, and at the same time, the law-making (or law-making) process and activities of authorized subjects in this area are the content, the essence of codification.