Traditionally, the principle of proportionality is defined as limiting State action to rational and reasonable means with the view to achieve a goal permissible under international law without unduly encroaching on the protected rights of another State, States, or individuals. The principle applies to the planning, as well as the implementation, of State activities. The application of the principle of proportionality is common in national constitutional and administrative law. A vast national jurisprudence exists in this regard. However, due to the plurality of approaches in the various national legal systems, it is hardly possible to draw any general legal conclusions from national experiences with the principle of proportionality. In this essay, after a brief account of the historical development of the principle of proportionality and an analysis of the relevant provisions of the United Nations Convention on the Law of the Sea (UNCLOS), it is considered whether the principle of proportionality only limits the competences of States—as traditionally envisioned—or enlarges them so as to meet community interests.