An appeal is a critique of first instance court´s work all the way until its final decision. In Slovenian legal order, appeal is a constitutional right, the enforcement of which obliges the legislator to also define reasons for appeal. It can be concentrated either on procedural (errores in procedendo) or substantive errors (errores in iudicando) of the judgement. As the latter results from the so called judicial syllogism, an appeal can refer to both premises from which the court´s conclusion originates, either the errors in applying substantive law (errores iuris), or the errors in ascertaining the facts of the dispute (errores facti). Therefore, the reasons for appeal are divided into three groups: severe violations of the procedural rules (divided into the so called absolute and relative violations), wrongly or incompletely ascertained facts of the dispute and the incorrect applicability of substantive law. A part of this thesis concentrates on the characteristics of the individual reasons for appeal. Slovenian Civil Procedure Act provides for the appellate courts to establish the existence of certain absolute procedural violations and the incorrect applicability of substantive law on their own motion. Other procedural violations and wrongly or incompletely ascertained facts of the dispute are to be established by court only if invoked by the appellant. The latter suggests the utmost importance for both parties, as well as the appellate court to understand the distinction among the different reasons for appeal. Namely, the appellant must, when invoking a reason for appeal that the court does not control on its own motion, explain and substantiate the existence of such reason. Therefore, this thesis also deals with the differentiation of the reasons for appeal, as well as the required argumentation in the appeal.