The works of Eliphas Levi on the science of the ancient Magi are intended to form a complete course, divided into three parts. The first part contains the Doctrine and Ritual of Transcendental Magic; the second is The History of Magic; and the third will be published later under the title of The Key to the Great Mysteries. Taken separately, each of these parts gives a complete instruction and seems to contain the whole science; but in order to a full understanding of one it is indispensable to study the two others carefully. The triadic division of our undertaking has been imposed by the science itself, because our discovery of its great mysteries rests entirely upon the significance which the old hierophants attached to numbers. THREE was for them the generating number, and in the exposition of every doctrine they had regard to (a) the theory on which it was based, (b) its realization and (c) its application to all possible uses. Whether philosophical or religious, thus were dogmas formed; and thus the dogmatic synthesis of that Christianity which was heir of the magi imposes on our faith the recognition of Three Persons in one God and three mysteries in universal religion.