This is a study of the circumstances and psychology of religious conversion during the last three centuries before Christ and the first four of the Christian era. The central theme is, of course, Christianity and its converts, of whom St. Augustine of Hippo is the great example; but Professor Nock also discusses the influence of philosophy, notably on Julian, and surveys the Non-Christian religious of the ancient world, the way in which they spread and the measure of their success. The book is written in untechnical language for the general reader, and it will be of equal interest to students of the Roman Empire and to students of the general problem of religious conversion.