A distinct characteristic of the judicial activity of integration courts is that it is aimed not only at resolving legal conflicts, but also at interpreting the law in order to fill the existing gaps. Filling legal gaps may be described as a key function of an integration court. This special characteristic leads to the phenomenon of judicial activism. The study of the case law of integration courts reveals the possibility to formulate activist legal findings using different methods of interpretation. The possibility to use the teleological method of interpretation, which is the most suitable in order to eliminate legal gaps, stems directly from the provisions of the Vienna convention on the law of international treaties. The analysis of the acts of the Court of Justice of the European Union allows to establish a strong correlation between activist approaches and the use of the teleological method of interpretation. However teleological interpretation does not necessarily mean the choice of the most progressive available options. Often the activism manifests itself in the search of a balance between the interests of the integration organization and its Member States. The Court of the Eurasian Economic Union develops activist approaches by using both traditional methods of interpretation and teleological interpretation as well as having recourse to constitutional traditions of the Member States.