The development of the Federal theology of the late sixteenth and early seventeenth centuries was a significant transformation in Reformed theological thinking. According to the Federal theologians, all of human history could be described using the rubric of a series of covenants, or foedera, beginning with a `covenant of works' in the perfection of Eden and concluding with the new covenant fulfilled by Jesus Christ in the New Testament. The new covenant was in effect the conclusion of the `covenant of grace', and it was this which united the Old and New Testaments into one continuous epic of God's grace and mercy. While John Calvin and many earlier Reformers discussed the importance of the postlapsarian covenant of grace, they never taught the Federal theology with its key identifying feature of a prelapsarian covenant.This book traces the prelapsarian covenant idea in Reformed theology from its first use by Zacharias Ursinus in 1562 to its flowering in 1590. Besides its origins, the implications of the Federal theology for Reformed thinking are made clear, and it is shown that the idea of covenant could have important implications for areas such as church and state, the sacraments, the Puritan doctrine of conversion, the Christian Sabbath, and the doctrine of justification and Christian ethics. The Federal theology is of considerable historical importance in intellectual history and forms the framework for much of the Reformed theology in the English-speaking world for three centuries.The doctoral thesis out of which this book developed won the Frank S. and Elizabeth D. Brewer Prize of the American Society of Church History.