It is crucial to ensure free testimony of witnesses so that the criminal procedure can easily be conducted. In order for the witness to give free testimony, the state is obligated to provide adequate protection. In this paper two categories of witnesses, threatened and vulnerable, have been elaborated in detail. Apart from defining the terms themselves, the way of treatment and participation of the mentioned categories of witnesses is explained. Particular attention among categories of vulnerable witnesses is devoted to the child as a witness. The paper also presents and explains the issues of opposing tendencies of the defendant's right to confront a witness of the prosecution and the rights of vulnerable and threatened witnesses in a special manner of participation and treatment in the proceedings themselves. Crown witnesses and undercover agents have been treated as the most frequent categories of threatened witnesses. Because of their properties, they often appear to be targets of criminal organizations. As such, it is necessary to protect them on a procedural basis and if that is not enough, it is necessary to provide protection of witnesses outside criminal proceedings, even after the criminal procedure is finished.