Zoroastrianism is of enormous importance in the history of religions. It can be traced back to a remote, possibly even Indo-European, past. This element links Zoroastrianism with the beliefs of ancient (Vedic) India, and survives as a subordinate part of what is one of the earliest revealed religions. Zoroaster's own teachings have moreover a highly spiritual and ethical content, which makes them a rewarding study in themselves. This book, now re-issued with a new introduction by Mary Boyce, is the first attempt to trace the continuous history of the faith from the time it was preached by Zoroaster down to the present day - a span of about 3,500 years. First taught among nomads on the Asian steppes, Zoroastrianism became the state religion of the three great Iranian empires and had a remarkable influence on other world faiths: to the east on northern Buddhism, to the west on Judaism, Christianity and Islam. With the conquest of Iran by the Muslim Arabs, Zoroastrianism lost its secular power but continued to survive as a minority faith. Despite its antiquity, it remains, therefore, a living religion.