The central focus of this edited collection is on the ever-growing practice, in liberal states, to claim exemption from legal duties on the basis of a conscientious objection. Traditional claims have included objections to compulsory military draft and to the provision of abortions. Contemporary claims include objections to anti-discrimination law by providers of public services, such as bakers and B&B hoteliers, who do not want to serve same-sex couples. The book investigates the practice, both traditional and contemporary, from three distinct perspectives: theoretical, doctrinal (with special emphasis on UK, Canadian and US law) and comparative. Cumulatively, the contributors provide a comprehensive set of reflections on how the practice is to be viewed and carried out in the context of a liberal state.