An important aspect of any constitutional theory is the state's power to punish transgressions of the law, or the ius gladii. Although Grotius never formulated a complete, comprehensive constitutional theory, traces of such a theory can be found in many of his writings not explicitly devoted to constitutional law. Punishment even plays an important role in his books on war (and peace), since to punish transgressions of the law is ranked among the just causes of war.Given the fact that a state may punish transgressions of the law – transgressions by individuals within and even outside the state, but also transgressions of the law by other states – the question may arise concerning the origin of such a right to punish. It will be shown that Grotius did not give the same answer to this question in his various works. As the right to punish is concerned, we find a theory that seems to be akin to the one of John Locke in the De iure praedae (around 1605), one akin to the theories of the Spanish late-scholastics in De satisfactione and De imperio (around 1615), and a theory coming close to what Thomas Hobbes had said on the ruler's right to punish in the De iure belli ac pacis (around 1625).Of course, Grotius can only have been familiar with the theory of the Spanish late-scholastics, since those of Locke and Hobbes were still to be written by the time Grotius had passed away.