This entry presents Hugo Grotius’ conceptualisation of territorial rights, as it can be articulated from his early philosophical works, De Iure Praedae and its twelfth chapter, published as an anonymous pamphlet under the title Mare Liberum. The first section is devoted to reconstructing the immediate context of both works as well as to offering a brief introduction to their overall argument. The second section delves into the Grotian concept and theory of territorial rights. Finally, the third and conclusive section addresses the relevance of Grotius’ theory in modern and contemporary debates on territorial rights.