Presentation of the final work are devoted to expert witness and expert witnesses in criminal proceedings. The paper presents evidence of criminal proceedings in general . The concept of evidence, direct and indirect evidence, evidence in a strict sense and evidence in a wider sense, as well as the notion of producing evidence and its phases are considered. Part of the work is dedicated to general issues of expert witnesses and expertise. It refers to the notion of expert witness and expertise, the similarity and the difference between expert testimony as evidence and testimony of witnesses, the duties of expert witnesses, persons who cannot be expert witnesses, and in particular the determination and the conduct of expert witnesses. The paper deals with psychiatric examinations, expertise on the severity of body injuries and traffic expertise. Psychiatric examinations are particularly demanding and complex because it is necessary to identify so-called internal facts - the mental state of the defendant at the moment of committing the criminal offense. Finally, in the conclusion of the final work, the results from all parts of the work that precede are summarized.