This book considers the proper nature and scope of criminal responsibility in the light of its institutional and political role. The book provides a systematic normative investigation of the nature and role of criminal omissions and criminal defences. Included are: a thorough account of the different ways in which mental disorders might ground defences, the nature of justification defences, the different kinds of excuse claim and the role that particular characteristics of the accused might have on the standards which the defendant must have met to escape criminal responsibility.