Grotius's great work, De Jure Belli ac Pacis, an 864-page work published in 1625, is still considered to be the single most important work in international legal theory. Grotius is the great modern defender of the Just War tradition, but he is also a kind of pacifist. This is an uneasy alliance within the same thinker. But such is the history of the Just War tradition, whose adherents maintained the same dual ideas: that war was evil, but that it could be, indeed must be, justifiable in certain cases. In this chapter I will attempt to explain how Grotius reconciled the various elements of his political and moral philosophy. And then, by building on Grotius's ideas I hope to provide the beginning of an account of a doctrine I will call “contingent pacifism.” Contingent pacifism is opposed to war not on absolute grounds but on contingent grounds, namely, that war as we have known it has not been, and seemingly cannot be, waged in a way that is morally acceptable. As we will see, jus ad bellum, the morality of initiating war, is thus dependent on jus in bello, the morality of waging war.