While recent years have seen a huge amount of work on the ethics of self-defence, this paper considers the ethics of defending others from harm. In particular, I assess the extent to which having the consent of victims of aggression (or at least the absence of refusal) is an independent moral requirement for permissibly defending them. While the consent requirement seems plausible in cases where there is only a single victim, I am interested in what we should say about more complicated cases that involve (i) multiple victims and (ii) where consent/refusal is mixed among members of the victim group. This question has considerable practical importance, since defensive wars will often have these two features. 

Several authors have recently argued that consent is practically irrelevant in multiple victim cases, or, at most, is an extremely weak requirement. I will argue, against the sceptics, for a qualified defence of the consent requirement. Put briefly, on the view that I advance, the consent or refusal of individual victims determines whether certain good effects of using defensive force can be appealed to in justifying defensive harms. The consent requirement is thus an internal component of the proportionality requirement. An important implication of my view is that what counts as sufficient consent for permissible defence will vary on a case-by-case basis, depending on the amount of defensive harm that requires justification.