This thesis deals with the topic of the crown witness, its position and role in criminal proceeding, with an emphasis on the Law on the Office for the Suppression of Corruption and Organized Crime as a lex specialis, which regulates conditions and procedure for granting its status. Crown witness is a member of a criminal organization to whom the court, at the request of the state attorney, assigns the position of witness in order to testify about organization’s structure, members and committed criminal offences. As such, it represents one of the exceptions to the principle of the legality of criminal prosecution, considering the fact that state attorney dismisses criminal charges or withdraws from the criminal prosecution, if that is proportional to the gravity of the committed criminal offence and the importance of the testimony of that person for detecting and proving criminal offences committed within a criminal association or their perpetrators. Criminal organizations readily respond to the innovative methods of the state's repressive apparatus, so cooperation with individuals is important for the full detection of perpetrators of criminal acts, and more importantly, planned criminal acts. Legal protection of crown witness is ensured not only in our legislation but also by international law, law of European Union and comparative law. In addition to this institute, this thesis also presents the institute of witness immunity, its current and previous unconstitutional legislative arrangement and similarities and differences with the institute of crown witness.