Originally published in 1933, this text is a study of the psychology and circumstances of conversion from about 500 BCE to about 400 AD. The text not only discusses early Christianity and its converts, but also examines non-Christian religions and philosophy, the means by which they attracted adherents, and the factors influencing and limiting their success. Christianity succeeded, the author argues, in part because it acquired and adapted those parts of other philosophies and religions that had popular appeal.