Appealing court decisions is an important element of the cassation review of court decisions and a component of the right to appeal a court decision. The issues of cassation appeal have repeatedly been in the focus of attention of scholars and practitioners, as evidenced by a significant array of works of monographic and dissertation nature. At the same time, the specificity of the cassation appeal is that this institution is a kind of trigger for the cassation review of court decisions that have entered into force. But at the same time, if the appellate review in the light of the case law of the European Court of Human Rights and the case law of national courts of appeal is defined as a minimum standard of appeal, the cassation appeal can be described as an exceptional (extraordinary) procedure. Therefore, the purpose of this article is to substantiate the signs of cassation appeal of a court decision as an exclusive, limited type of review of court decisions, to determine the task of this type of appeal and to separate its functions. The article examines the institute of cassation appeal of a court decision as one of the types of review of court decisions provided by the legislation of Ukraine. The signs of cassation appeal of a court decision have been studied and evaluated, which include: appeals of court decisions that have entered into force; constitutionally defined, generally limited nature of the cassation appeal; exclusivity (extraordinary) cassation appeal, which embodies an additional tool to ensure the justice of court decisions; verification of a court decision that has entered into force by another composition of the court, different from the composition of the court in the first and appellate instances; conditionality in accordance with the procedural law, taking into account the constitutional provision on the possibility of cassation appeal only in cases specified by law; unconditionality of the prohibition of cassation appeal; one-time cassation appeal. It is proved that the task of cassation appeal is a mechanism of procedural law mechanism of appeal to the court of cassation with a cassation appeal on the basis of free will of a person as a prerequisite for further cassation review of a court decision that has entered into force. Settlement of the possibility of cassation appeal of a court decision, which came into force, restrictive provisions of constitutional and legislative norms made it possible to talk about two functions of cassation appeal - regulatory (in case of non-compliance of cassation appeal with procedural law) and permissive (subject to cassation appeal procedural norms-filters).