ENThe chapter covers an analysis of two cooperation procedures where Lithuanian courts participate: cooperation with the European Court of Human Rights in accordance with Protocol No. 16 to the Convention for the Protection of Human Rights and Fundamental Freedoms (Part 1) and cooperation with the Court of Justice of the European Union under Article 267 (Part 2) of the Treaty of the Functioning of the European Union. The article carries out a survey of the provisions of the Convention, Protocol No. 16, and provisions of the EU legislation, as well as the jurisprudence of the ECHR and CJEU, and the Lithuanian legal acts which regulate the work of Lithuanian courts and establish legal grounds for cooperation between the Lithuanian courts and the ECHR and CEJU. The aim is to establish the most recent changes in the role of the Lithuanian courts related to Lithuania’s membership in the European Union and the status of a contracting party to the Convention. The article touches upon the essential differences between an advisory opinion procedure at the ECHR and a preliminary ruling procedure at the CJEU as much as it is related to the legal grounds of these procedures. The study suggests the following conclusion: as Protocol No. 16 came into force recently, the ECHR case law will show how the advisory opinion procedure will be put into practice and what most serious difficulties the courts of the High Contracting Parties will face in the near future. An analysis of the jurisprudence of the CJEU and the Lithuanian courts proves that Lithuanian courts benefit from the cooperation procedure with the CJEU under the procedure envisaged in Article 267 TFEU with high efficiency and raise new questions on the interpretation and application of the European Union law. [From the publication]