What is Theurgy? According to the perennial wisdom of the ancient sages, Theurgy is the exalted goal of communicating with, and bringing down to earth, planetary spirits and angels: the gods of wisdom and light. And only a knowledge of the inner meaning of their hierarchies and an absolutely pure and unselfish mode of life can lead to the acquisition of the powers necessary for entering into communion with them. The present work contains a series of epistles that the ancient Neo-Platonic theurgists Iamblichus (245-325 a.d) and Porphyry (234-305 a.d) exchanged. Apart from the translation into English and annotations of the modern Neo-Platonic scholar and theosophist Alexander Wilder, the present edition also benefits from the Introduction and annotations that Thomas Taylor provided in his own and alternative translation of this work, plus still further annotations and a new Prologue by Sonchis Triacorda, thus providing more than 100 pages of additional text. This work is an invaluable help for the attainment of the first requisite of Theurgy, i.e., true knowledge of the inner meaning of the divine hierarchies. For the attainment of the second requisite, however-i.e., an absolutely pure and unselfish mode of life-one should perhaps not look at books but somewhere else.