This article analyses military activities in the Exclusive Economic Zone (EEZ) from a legal point of view. It starts from the discussion of the principles of Mare Liberum and Mare Clausum, which are at the basis of the United Nations Convention of the Law of the Sea (UNCLOS). This latter is the main instrument regulating the relations among states at sea. The tension between the two principles reflects the tension between coastal State control and maritime State that dominates the whole discussion on which this article is written. The analysis is supported by a recent example, namely the NordBalt case that clearly shows both the uncertainty of the issue and the relevance of the topic in the relations between states.