Essentialism is a powerful theory about Christian identity, because it reduces various complex questions to one issue: the determination of an invariable essence. What distinguishes Christianity from other religions? What is authentic Christian faith and what is contrary to it? What is the unity of Christianity beneath all the different forms of expression? What is its identity through time? Which aspects of faith are indispensable? All these questions are answered at once by essentialism. However, the price to be paid for this simplification is high. It implies that differences among Christians themselves cannot be essential; that Christian history should contain some kind of homogeneous development of the essential content of faith; and finally, that church unity can only come about when all agree about the essence. Should we not rather look for an alternative way to think about Christian identity? In this book, modern philosophical analyses of the identity of objects and persons are used to develop an alternative which can do more justice to the differences and changes within Christianity.