Johannes Cocceius (1603-1669) was prominent Bible scholar who taught at the universities of Bremen, Franeker, and Leiden. As a gifted linguist, he produced a Hebrew lexicon, commentary related to every book of the Bible, and several theological treatises. Cocceius's contributions to covenant theology simultaneously sparked theological controversies and further fruitful dialogue for understanding the progressive nature of salvation history. The Doctrine of the Covenant and Testament of God describes the entire biblical history as a series of events by which an original covenant of works is gradually annulled, bringing new phases in the history of the covenant of grace. He shows that God's standard way of relating to mankind is through covenant, which, at its heart, is friendship with God. Casey Carmichael's translation of Cocceius's book is monumental, providing the first English edition of a work that helped shape Reformed theology for centuries. Historical theologians have long noted Cocceius's work as a crucial text in the development of federal theology, and now this translation will open access to a wider range of readers and is sure to spur further interest and research in Reformed expositions of covenantal thought. The introduction by Willem J. van Asselt, the world's leading scholar on Coccieus's life and theology, provides the historical context for understanding the importance of the book and a summary of the significant contributions it made to Reformed theology.