To treat some human beings as less worthy of concern and respect than others is to lose sight of their humanity. But what does this moral blindness amount to? What are we missing when we fail to appreciate the value of humanity? The essays in this volume offer a wide range of competing, yet overlapping, answers to these questions. Some essays examine influential views in the history of Western philosophy. In others, philosophers currently working in ethics develop and defend their own views. Some essays appeal to distinctively human capacities. Others argue that our obligations to one another are ultimately grounded in self-interest, or certain shared interests, or our natural sociability. The philosophers featured here disagree about whether the value of human beings depends on the value of anything else. They disagree about how reason and rationality relate to this value, and even about whether we can reason our way to discovering it. This rich selection of proposals encourages us to rethink some of our own deepest assumptions about the moral significance of being human.