The studies in this book set out a bold thesis: that there is a distinct movement of thought within the period of the Protestant Reformation in Europe that may be called ‘Covenant Ecclesiology’. The proposal was made during 2017, a year that was named as ‘Reformation 500’, marking half a millennium since Martin Luther issued his 95 theses. The year hosted many reflections on the Reformation from three of its ‘children’ – Lutheran, Reformed and Anglican. This collection of studies, originally papers given at a conference at Regent’s Park College, University of Oxford, identifies a fourth child of the Reformation, whom other siblings have sometimes regarded as a ‘wild child’. It is, however, less a single church than a diverse movement, born in the Reformation and its immediate aftermath in the form first of Continental Anabaptists, and then of English Separatists from the new Church of England. By the early years of the seventeenth century many Separatists had morphed in England into General Baptists and Independents, later Congregationalists, and on the Continent Anabaptists had developed into a variety of groups, of whom Mennonites are best known today. It was characteristic of members of all these groups to pledge to ‘walk together’ under God in a covenant that was marked by two dimensions – a vertical vector of relation with God and a horizontal vector of relation with each other. While Anabaptists are sometimes named ‘the radical Reformation’, these studies propose that various radical offsprings of the Reformation are best characterized by what is common to them – an ecclesiology at whose centre is covenant, with Christ as the covenant-maker.