The theme of this diploma thesis is the investigation in the criminal procedural law, i.e. the course of that stage, from its beginning until the end. First part of this paper sets out some general information about the investigation, of its purpose and conditions for initiation. Also, there are given the main subjects of the process, their roles, powers and duties during the procedure. The main part of the paper tells us about the way of executing actions during the investigation, warrants of the State Attorney and actions of the investigator, but also about the rights of the defendant and the injured party, which they can claim during the process, and how they can accomplish that. Furthermore, there is explained the importance of taking some certain evidentiary actions in the process and the way of establishing the facts, on which the evidence can be based. The last part of the paper includes the interruption, suspension and termination of the investigation, that is, there are clarified situations when a decision about that can be made, and the meaning of it for the further process. The purpose of this paper is to emphasize the importance of the investigation as a part of the criminal proceeding and its influence on further actions and making the decisions.