This book examines the secret role of British and German Christians in the Cold War, both as non-governmental envoys and as members of covert intelligence operations. Based on archival sources, including those of the Stasi together with interviews with some of those involved, it demonstrates the way in which religion was used as a tool of psychological warfare. During the 1960s, the concept of Christian-Marxist dialogue was espoused by Church leaders and appropriated by politicians. In the GDR, Ulbricht used Christian-Marxist dialogue to quell opposition to his regime; in the West, politicians encouraged a policy of détente which led to the erosion of communist ideology. As the seeds of Ostpolitik were sown, Christians tunnelled their way beneath the ideological barriers of the Cold War in the name of reconciliation while secretly establishing subversive networks. At the same time, they provided political leaders with a hidden channel of communication across the Iron Curtain. This book examines the 1965 Coventry Cathedral project of reconciliation in Dresden, the work of Paul Oestreicher, and the activities of the German Christian organisation Aktion Sühnezeichen. In doing so, it reveals the complexity of the Cold War world in which both sides appeared to hold out the hand of friendship while secretly working to eliminate the enemy.