Introduction. At the current stage of development of criminal procedure and forensic science, the sphere of criminal justice is often considered from the perspective of an activity-based approach, i.e., as the activities of individual subjects (investigator, prosecutor, suspect (accused), defense counsel, investigating judge, court, etc.) and their interaction. Similarly, a large number of proposals in the literature are related to the improvement or optimization of their activities with regard to the general principles of criminal proceedings. This article is no exception and is aimed at clarifying the approaches to understanding the activities in the field of criminal justice and their regulation (formalization). Summary of the research results. The article makes an attempt to summarize the existing views on the content of such concepts as criminal procedural activity, activity of an investigator, a prosecutor, an investigating judge and other participants to criminal proceedings. The author proposes the term "activity in the field of criminal justice" as a generalized term which reveals the social nature of the activity of investigation and trial of criminal offenses. The author also proposes an approach whereby regulatory and legal regulation, other types of social regulation and organizational and tactical recommendations are considered as means of formalizing activities in the field of criminal justice, i.e., those aimed at streamlining them and bringing them to a certain standard. At the same time, it is proposed to differentiate these measures depending on the degree (rigidity) of formalization. Conclusions. Based on the results of the study, the author concludes that formalization of activities in the field of criminal justice should be understood as the process of streamlining the actions and decisions of participants to criminal proceedings through their legal regulation, established ethical norms, and also such means as planning of activities by the subject and application of the rules of a recommendatory nature which are concentrated in the provided algorithms and programs. These means of formalization have different legal nature, but they can still be considered in the same order in accordance with their function in the field of criminal justice, which provides for the possibility of their grouping.