The doctrine of believers' union with Christ has undergone a renaissance in recent years. Evangelicals are increasingly fascinated by this previously neglected doctrine--a doctrine with wide-ranging implications for the whole of Christian theology. Drawing on his extensive teaching and research experience, theologian Robert Peterson has written what may be the most comprehensive theological treatment of union with Christ to date, highlighting the Spirit's crucial role in uniting God to his people. In part one, Peterson explores the Bible's teaching, carefully examining a host of relevant passages from both testaments that speak to what it means to be "in Christ." In part two, he moves on to systematic theology, constructing a cohesive doctrinal framework aimed at bolstering the church's faith and worship.