Jean Baubérot’s ideal secularism is not a political reality anywhere and never has been. There are a variety of configurations even in states that describe themselves officially as secular. They do not have identical laws, constitutions, or ways of relating to religious institutions. There are also some states that are not officially secular, but are in many ways secular in practice. ‘Conceptions of secularism’ discusses the continuing debate that rages over the definition of ‘secularism’ between philosophers, sociologists, political scientists, campaigners, politicians, and lawyers who all disagree with each other about what it should and should not mean. All these conceptions of secularism influence each other and all have their partisans and their critics.