Introduction Peace is better than war. It takes two to fight. These are truisms: they’re true, but so obvious that they’re not usually worth stating. But they swiftly generate conundrums in the ethics of war in general, and the Ukraine conflict in particular. We can learn something, in my view, from thinking about these conundrums. But we may need to tackle the understandable concern that it’s unhelpful to explore them at a time when energy and attention levels are flagging in the international community, even though Ukraine remains under attack from Russia and arguably requires all the support, moral and otherwise, that it can get. In some circumstances, indulging in more theoretical speculations—the kind of speculative and hypothetical thinking that forms the daily diet of philosophers of war—may come across as being objectionably detached, or perhaps as just another way of being a useful idiot. These worries deserve careful consideration, not hasty dismissal. If there’s to be a place for serious philosophizing about war, it needs to be reconciled with the more engaged concerns of …