This is a book about relationships and duties. It defends the thesis that we owe duties to those with whom we enjoy relationships on account of those relationships, and specifically on account of their value. If that seems an obscure thesis, that is only because we normally individuate our relations with family members, friends, associates and so on, and because the claim that relationships ground duties is the terse expression of an argument I pursue at length. In fact, we generally believe our relations with our nearest and dearest are valuable because they promote our flourishing, as well as theirs, and it seems a matter of common sense to think that the duties we owe them have something to do with that flourishing. These relationship-based duties-associative duties-make up most of the substance of our moral lives. We do things with, to and for our children, parents, friends, colleagues, team members and even-or so I argue-our fellow citizens. We spend most of the time most of our life interacting with people through the medium of the relationships we share with them-think about how you have spent your time today. Such is the richly complex nature of human social life that the most salient encounters we have with other people tend to be through the medium of the social roles through which they connect with us.