The unity of the legal order is the foundation of the rule of law. It also implies the internal harmony of decision-making, ie. the absence of contradictory court decisions in the unified legal system. In order to realize this ideal, it is necessary for the legal system to foresee that legally binding and final individual legal acts mutually bind state bodies. The unity of the legal system can be only achieved when the system provides that conviction judgment rendered by a criminal court bind civil court in the subsequent civil proceedings. Civil courts should be also bound by a decision rendered by a criminal court if the defendant is acquitted of the charge, in case criminal court has solved some preliminary question that is important for deciding in civil proceedings. Such a system exists in Austria and Serbia. In principle, a verdict rendered by a criminal court should produce effects erga omnes. On the other hand, in Germany and Anglo-Saxon legal systems, the principle of independence of criminal and civil justice applies. However, the difference between the previous and the latter system is not as significant as it seems at first glance, because the judgment of the criminal court in civil proceedings has a significant probative value. From the point of view of the Constitution of Serbia, as well as the European Convention on Human Rights and Fundamental Freedoms, the principles of independence of the courts in making decisions, the requirement that a court must only be bound by the Constitution and the law are not an obstacle for the legislator to determine that the final judgment of the criminal court binds the civil court. The principle of res judicata, which forms one of the foundations of the rule of law, is much broader in Anglo-Saxon than in Euro-continental law. This particularly applies to the application of the institute issue or collateral estoppel which derives from the Roman principle of venire contra factum proprium. The principle serves to prevent substantial injustice. The principle of the rule of law requires legal certainty and predictability which implies the absence of contradictory court decisions in a unified legal system. In order to avoid the possibility of making contradictory court decisions, it is necessary to reexamine the ambit of the res judicata principle and to extend the application of the principle of venire contra factum proprium and preclusion in order to achieve procedural fairness.