Subject of this diploma paper is investiogation and inquery in Croatian criminal procedure law (NN 152/08., 76/09., 80/11., 121/11., 91/12., 143/12., 56/13., 145/13., 152/14., 70/17., 126/19., 126/19.). Investigation and inquery are substages of criminal preliminary procedure and such as they are alanized and researched in this work. The goal of this work is to point out the importance of the proper conduct of investigation and inquery and the roles played by entities such as the state prosecutor, investigation judge and coroner in this phase of procedure. During the investigation and inquery, it is necessary to gather data and evidence necessary to make a decision on the indictment or to suspend the proceedings, as well as evidence that is likely to not ne possible to repeat at the hearing or there is a danger of their difficulty to repeat. This is also the purpose of undertaking an investigation and inquery. Thus, these are the stages of the preliminary procedure in which the same evidentiary actions are taken, but on the other hand, the rules related to their implementation are different, and which will be discussed in more detail in this diploma paper.