We prize loyalty in our friends, lovers and colleagues, but loyalty raises difficult questions. What is the point of loyalty? Should we be loyal to country, just as we are loyal to friends and family? Can the requirements of loyalty conflict with the requirements of morality? In this book, originally published in 2007, Simon Keller explores the varieties of loyalty and their psychological and ethical differences, and concludes that loyalty is an essential but fallible part of human life. He argues that grown children can be obliged to be loyal to their parents, that good friendship can sometimes conflict with moral and epistemic standards, and that patriotism is intimately linked with certain dangers and delusions. He goes on to build an approach to the ethics of loyalty that differs from standard communitarian and universalist accounts. His book will interest a wide range of readers in ethics and political philosophy.