Traditionally, the notion of defeat has been central to epistemology, practical reasoning, and ethics. Within epistemology, it is standardly assumed that a subject who knows that p, or justifiably believes that p, can lose this knowledge or justified belief by acquiring a so-called ‘defeater’, whether that is evidence that not-p, evidence that the process that produced her belief is unreliable, or evidence that she has likely misevaluated her own evidence. Within ethics and practical reasoning, it is widely accepted that a subject may initially have a reason to do something although this reason is later defeated by her acquisition of further information. However, the traditional conception of defeat has recently come under attack. Some have argued that the notion of defeat is problematically motivated; others that defeat is hard to accommodate within externalist or naturalistic accounts of knowledge or justification; and still others that the intuitions that support defeat can be explained in other ways. This volume presents new work re-examining the very notion of defeat, and its place in epistemology and in normativity theory at large.