This article considers the admissibility and procedural aspects relating to the filing of counterclaims in international law, with particular reference to bodies exercising jurisdiction under the United Nations Convention on the Law of the Sea —namely the International Court of Justice, International Tribunal for the Law of the Sea and Arbitral Tribunal instituted under Annex VII to this Convention. Counterclaims in the context of UNCLOS tribunals raise specific questions. For instance, the ambiguity concerning the rules applicable to counterclaims presented in Annex VII proceedings has recently been dealt with by an Annex VII Arbitral Tribunal in The ‘Enrica Lexie’ Incident case. The approach of the Tribunal needs careful consideration. In the M/V “Virginia G” Case, the approach taken by ITLOS questions the manner of interpretation of the ‘direct connection’ requirement in the context of UNCLOS cases. For this purpose, the present study of counterclaims provides a comparative analysis of the rules and practices of the three aforementioned bodies.