Intolerance of ideas different from one’s own seems to be a common attitude among human beings and, at the same time, something that seems to be more pronounced in recent years. In this volume, political theorists and philosophers consider some of the historical preconditions of modern intolerance and debate the sources of its recent manifestations.From theories of religious intolerance during the Reformation to the contemporary suppression of religious symbols; from homophobia to attempts to ban it; from populism on the right to “cancel culture” on the left—this book covers a variety of forms of intolerance, analysing not only its consequences but its causes and implications. Some of the chapters suggest means by which democracies may, through popular and judicial measures, defend themselves against intolerance, while others probe the philosophical grounding of intolerance in epistemological and metaphysical doctrines such as self-evident truth, divine revelation, inner illumination, naïve realism, and the moral relativism attributed to analytic philosophy and postmodernism.The chapters in this book were originally published as a special issue of Critical Review.