This thesis is an interdiscipinary study about the nature and causes of transsexuality and an attempt to formulate a Christian ethical response to it, a subject which until now has received no extended academic attention from a Christian perspective. There are two aims. The first is to examine what the Christian theological tradition has to say about transsexuality. the second is to explore what the experience of transsexual people has to say to the Church, and to the formation of its theology and ethics. It is a survey of the evidence for the existence of transsexuality prior to the twentieth century, when it was first recognised and described. It explores the experience of transsexual and some transgendered people in Britain today. It pays particular attention to their encounters with and within the Church. It investigates how those transsexual and transgendered people who profess Christian faith use the Bible and relate to the Christian tradition as they attempt to understand their condition better, and try to come to terms with the theological issues that this process of reflection raises - an example of 'ordinary theology'. It then examines what the Bible and the Christian tradition themselves might have to say about transsexuality, and about those same far-reaching issues, which include the significance of the human self, of embodiment and of sex, gender and sexuality. It draws in particular on the foundational theology of Irenaeus, Tertullian, Origen and Gregory of Nyssa and on the writings of four contemporary theologians: Lisa Sowle Cahill, Elaine Graham, Susan Frank Parsons and Rowan Williams. At the heart of the study are seven detailed case studies of transsexual or transgendered British Christians, but I also draw on a personal engagement with around twenty five others over a period of almost thirty months.