In the first half of this Chapter I will look at some of the most interesting ancient responses to the question: when is war just. Then in the second half of the Chapter I will assess these various responses for normative guidance today. I will draw often on ancient sources in order to show how old the controversy is and how often the answers were different from but relevant to our situation today. My thesis is that from the earliest of times the only relatively sure grounding for a just war is defense of those who are oppressed, either oppressed by aggressors from without or oppressors from within.