We emerge from certain activities with an altered sense of self. Whether returning from a warzone or from an experience as common as caring for an aging parent, one might remark, “I’m not the same person I was.” I argue that such transformations are relevant to debates about what morality requires of us. To undergo an alteration in one’s self is to make a special kind of sacrifice, a sacrifice of self. Since projects can be more or less morally obligatory (...) to the extent that they require more or less sacrifice, we must incorporate these unique sacrifices into any accounting of the contours and limits of moral obligation. But sacrifices of self pose a special difficulty for any such accounting, precisely because of their transformative nature. Unlike most other sacrifices, they cannot be analyzed entirely in terms of wellbeing. Using real-world case studies and examples, I argue for the existence of two types of sacrifice of self, involving changes in identity and moral agency. I argue that sacrifices of self require particular attention because they may be extra difficult to compare with other costs and with moral gains. (shrink)