Object of research: the legal relationship that arises, develops and ceases when the parties prosecute and defend their powers at the stage of pre-trial investigation of criminal offenses. Purpose: to develop the scientific, legal and functional foundations of the institute of parties of pre-trial investigation, aimed at improving the provisions of the Criminal Procedural Code of Ukraine regarding the optimization of their procedural activities. Methods: general and special methods of cognition, in particular, dialectical, logical-semantic, logical-legal, comparative-legal, formal-legal, sociological, statistical, etc. Theoretical and practical results, scientific novelty: it is suggested at the legislative level to clearly define the criminal procedural functions of all the pre-trial investigation authorities and their participants, who defend their personal or represented interests related to the resolution of the criminal legal conflict in essence, and on on this basis, it is right to form a stable group composition of each party to the criminal proceedings; the system of procedural actions and decisions of the prosecutor, which he is obliged to perform during the preparation and official registration of the indictment, is determined; it has been proved that the monopolization of the lawyers of Ukraine with the right to protect the suspects charged with criminal proceedings poses a great threat to the field of combating criminal offenses, which requires the extension of a range of lawyers who may be allowed as defenders in these proceedings; It was considered necessary to introduce to the CPC of Ukraine the institution of mandatory participation of the representative-advocate of the victim on the charge side with payment of legal services provided to him to a victim of a criminal offense solely at the expense of the state; the necessity of abolishing the criminal procedural institute for the refusal of the suspect, accused of the services of the defender in connection with the desire to protect himself personally, because the absence on the side of the protection of a professional specialist in the field of law excludes a full-fledged competition of the parties, is connected with the deep legal analysis of forensic evidence being investigated them; Improved: scientific provisions on supplementing the criminal proceedings of Ukraine with a new pre-trial stage entitled "prosecution"; scientific approaches to the inappropriate use of the term "protection" in the CPC in different ways: to determine the fundamental (general-procedural, through) function of protecting the rights and legitimate interests of a suspect, accused (defendant), acquitted, convicted; to determine the obligatory function of all power subjects of criminal proceedings to ensure the rights and legitimate interests of all its participants; scientific proposals on obligatory assignment of the victim as a direct participant in a bilateral criminal-legal conflict: the offender - the victim of the offense, to the party of the charge. Practical significance: the results obtained can be used in the research area for further research on the activities of the prosecution and defense parties in the pre-trial investigation from the point of view of their activities on the basis of the principle of competition, in the field of law enforcement as recommendations on the activities of the parties during the investigation of criminal offenses, in the legislative sphere to improve the criminal procedural legislation of Ukraine regarding the procedure for the formation and operation of prosecution and defense parties in the pre-trial investigation. Sphere of use: in the educational sphere during the teaching of disciplines "Criminal Procedure of Ukraine" and "Criminology", in the preparation of textbooks, manuals and teaching materials from these disciplines.
