The judgment of the Court of Justice in the Achmea case evoked significant repercussions regarding the application and operation of the bilateral investment treaties (BITs) concluded between EU Member States. As a result of this decision, EU Member States have decided to terminate almost 190 intra-EU BITs. Nevertheless, full implementation of the Achmea judgment remains a complex issue, entangled in political and legal controversies concerning intra-EU BITs which have been present for more than a decade. On a more general level, the implementation process is simultaneously entwined in two other significant debates: the specifics of the rights of investors, and the relationship between EU law and international law.

This article analyses the practice of the Polish administrative courts with respect to application of the Vienna Convention on the Law of Treaties, based on a case study of the judgment of the Voivodship Administrative Court in Warsaw of 6 May 2014 (case no. II SA/Wa 117/14), which concerned the recognition of distance learning degrees awarded by Ukrainian universities pursuant to the 1972 Prague Convention. It is argued herein that the reasoning of the court suffers from four major drawbacks: 1) it is at variance with the text, object and purpose of the Prague Convention; 2) it does not take into account the practice in the application of that treaty; 3) it misinterprets the silence of the preparatory work to the Prague Convention on certain issues; and 4) it is inconsistent with international judicial decisions as regards the interpretation of the “special meaning” of one of the terms used in the Convention.

This article explores the legal principles that govern the interpretation of “secondary instruments” in international law. A “secondary instrument” under international law is, for the purposes of this article, a written document adopted by a body empowered by a treaty to take action with respect to the treaty, but which is not itself a treaty. Such instruments find increasing application in international law. The article specifically examines the interpretation of secondary instruments arising in five settings in international practice: the United Nations Security Council, the International Maritime Organization, the International Seabed Authority, the International Whaling Commission, and conferences/meetings of the parties under multilateral treaties. This selection of practice will serve to illustrate principles of interpretation across a range of international institutional settings for the purpose of determining the rights and obligations of state-parties to a treaty regime.