What does it mean to be sad? What difference does it make whether, how, and why we experience our own, and other people's, sadness? Is sadness always appropriate and can it be a way of seeing more clearly into ourselves and others? In this volume, a multi-disciplinary team of scholars - from fields including philosophy, women's and gender studies, bioethics and public health, and neuroscience - addresses these and other questions related to this nearly-universal emotion that all of us experience, and that some of us dread. Somewhat surprisingly, sadness has been largely ignored by philosophers and others within the humanities, or else under-theorized as a subject worthy of serious and careful attention. This volume reverses this trend, presenting sadness as not merely a feeling or affect, but an emotion of great moral significance that in important ways underwrites how we understand ourselves and each other.