Marcion is one of the most intriguing yet elusive figures in early Christian history. It is proof of his prominence that, among the diverse forms of Christianity that flourished in the second century, his was the most frequently and forcefully attacked by anti-heretical writers, and was apparently perceived as the most dangerous. Marcion has likewise interested modern scholars, not only because of the peculiarities of his teachings but also because of his possible influence on one of the most important developments in the early church, the formation of the Christian Bible. In that connection, Marcion has commanded attention on two major topics: the church’s appropriation of the scriptures of Judaism (which it came to call the ‘Old Testament’), and the emergence of a canon of specifically Christian scriptures (a ‘New Testament’).

It is impossible in short space to do justice to the many difficulties that beset the study of Marcion and his influence. It has not yet become entirely clear either what Marcion taught or why he taught it. Some of his salient convictions are well known, but it remains uncertain how they arose, cohered or intersected the convictions of others. The old question whether Marcion should be regarded as a biblical theologian or as a Gnostic (or philosophical) teacher has not been answered, and cannot be answered in those terms. But, by situating Marcion within second-century Christianity and the issues that preoccupied it, we can go far towards making his activity intelligible and evaluating his role.