This chapter discusses Jewish ethics and war. It first turns to ancient and medieval Jewish sources to describe what they tell us about the ethics of going to war (jus ad bellum) and of waging war (jus in bello)—especially Deuteronomy 20–21 and Maimonides' code of Jewish law, the Mishneh Torah. Recognizing that until the founding of the modern State of Israel, Jews fought in armies governed by non-Jewish rulers, it then examines a nineteenth-century book intended to instruct Jews about how to act in military service. The overriding principle in that book and in the few other Jewish treatments of the ethics of war during the last two thousand years was “the law of the land is the law,” and that law was determined by the non-Jewish ruler. What happens, though, when Jews determine the law of the land? The chapter examines some Jewish writings published just before and after the establishment of the State of Israel that anticipate this issue. It discusses the doctrine of “purity of arms” that has shaped Israeli military ethics, the role of the military rabbinate, the Code of Ethics which now governs Israel's military actions, the ethics of fighting terrorism, and the ethics of seeking peace.