St Cyprian, third-century bishop of Carthage, developed a theory of church unity almost universally accepted up to the European Reformation: to be a member of the Body of Christ you needed to be in communion with a priest who was in communion with a bishop who in turn was in communion with all other bishops in the world. But, how could you discern who was a legitimate bishop? And, on what kind of issue would it be right to break off communion? Additionally, could self-authenticating ministries, like those of martyrs and confessors who had suffered for the faith, supersede this order? Finally, did the Church need, and in what form, a universal bishop who could guarantee the integrity of the network of bishops?

St Cyprian wrestled with these questions in his letters and treatises, selected and translated in these companion volumes. Each volume contains an introduction to the two principal controversies that spurred St Cyprian to write his defense on church unity: first, the readmission to the Eucharist of those Christians who had lapsed or fallen in the persecution under Emperor Decius; and second, the sacramental validity of baptism in heretical and schismatic communities.

They are questions that continue to arise in various forms in the contemporary Church, and thus, these companion volumes are of ultimate value to the state of current Christendom.