In October 2003, Croatia declared an “Ecological and Fisheries Protection Zone” in the Adriatic Sea. However, in June 2004 Croatia decided to delay the implementation of that Zone for the European Union (EU) Member States. Then, in December 2006 it decided to implement the Zone fully from 1 January 2008—only to discontinue its application to EU countries from 15 March 2008. The developments and underlying reasons for the changing jurisdictional picture in the Adriatic Sea are the subject of this article. Key Adriatic Sea features, trends in uses of its living resources and maritime space, and resource conservation and marine pollution concerns are presented. Developments leading to recent national legislation and positions on maritime jurisdiction by Croatia as well as Italy and Slovenia are discussed. These regulations, positions and developments are assessed from the perspective of the law of the sea. Relevant policy perspectives, including aspects of EU membership, are included.