The "Sepher Yetzirah," or "Book of Formation," is perhaps the oldest philosophical treatise which is yet extant in the Hebrew language. The great interest which has been evinced of late years in the Hebrew Kabalah, and the modes of thought and doctrine allied to it, has induced me to translate this volume from the original Hebrew texts, and to collate with them the Latin versions of mediaeval authorities. Three important books of the "Zohar," or "Splendour," which is the great storehouse of Kabalistic teaching, have been for the first time translated into English by that skilful and erudite Kabalist, my fellow student in occult science, MacGregor Mathers, and the "Sepher Yetzirah" in an English translation is almost a necessary companion to these even more abstruse disquisitions: the two books indeed mutually explain each other.