It The article analyses the origins and essence of the stare decisis principle, examines its specific features and formulates its concept. It is substantiated that the principle of stare decisis is a primary principle of procedural law by its structure, which has a cross-sectoral nature and is applicable in court proceedings regardless of the jurisdiction (administrative, criminal, civil, etc.) of the court, addresses the judiciary (not other participants in the court proceedings) with a mandatory requirement to adhere to the legal position formulated in previous relevant court decisions in new court decisions in order to ensure the unity and consistency of judicial practice, its certainty and predictability, which makes it possible for the subjects of legal relations to adjust their legally significant actions (activities) in the future. The authors makes a comparative analysis of the principle of «stare decisis» in the AngloAmerican and Romano-Germanic legal systems. It is proved that this principle in the Anglo-American legal system is interpreted in the sense of «to stand on what is set by the court», and in the Romano-Germanic legal system – «to stand on what is set by law». The authors argues that a court decision is always related to the resolution of a dispute, but in the Anglo-American legal system, a court dispute is related to law, and in the Romano-Germanic legal system, it is related to a violation of law. The effect of the principle of stare decisis in the Anglo-American legal system is manifested in the rule: «precedents are not overruled», even if they are outdated, they still remain in force. In fact, the same rule applies in the Romano-Germanic legal system, because the legal positions set out in the decisions of the Supreme Court are also not cancelled, but rather «departed from» by the court. In the Anglo-American legal system, the principles of law are embodied («live») in judicial doctrine and precedents, which activates judicial rule-making, while in the Romano-Germanic legal system, the principles of law are objectified in legislation, so the principles of law actually become legislative norms, which reduces the discretion of judicial discretion in this legal system. The authors concludes that the principles of law do not adapt to social relations; on the contrary, legislative norms are developed, grouped and adjusted in accordance with the requirements and content of the principles of law. Key words: stare decisis principle, judicial proceedings, principles of law, legal systems of the world, constitutional mechanism of the state, constitution of the state, sources of law, Roman law, judicial precedent.