The study fills a gap in Russian criminal procedure law science as to the study of the system of reviewing judicial decisions that have not entered into legal force in people’s democracies and its further reform during the post-socialist transition (using the Republic of Bulgaria as an example). During the transformation of proceedings in the second instance court, a return to the traditional institutions of the Bulgarian judicial system and criminal proceedings was carried out. This was achieved by reinstating appellate courts and appellate proceedings, as well as by aligning the criminal procedure legislation governing second instance court proceedings with the generally recognized principles and norms of international law. The paper highlights the general provisions (conditions) for the construction and operation of methods for monitoring judicial decisions, which serve as criteria for comparing proceedings in the second instance court with modern appellate proceedings. Some of these general provisions have not undergone significant changes in the course of judicial reform. Institutional transformations have occurred in the legal and factual review of judicial acts in the appellate court. The shortcomings of the Soviet model of proceedings in the court of second instance were overcome by establishing in appellate proceedings of the absence of grounds for overturning or amending a court decision; the possibility of conducting a judicial investigation; the right of the appellate court to render a verdict; and the elimination of the institution of directives from a higher court when remanding a case. Modern appellate proceedings ensure the right to a fair trial, which ensures effective restoration of rights.

   It is necessary to reform the current legislation by bringing it into line with the legal positions of the European Court of Human Rights, including in terms of the questioning of witnesses in the appellate court.