Despite growing evidence for the range of Ismaili esoteric interpretations of scripture and legal pronouncements, and of a variety of sciences, scholarly exploration has not, so far, provided any clear account of this doctrine. Yet, from its beginning as a separate form of Shiism, nearly all observers were aware that the ??hir/b??in distinction advocated by the da’wa implied some type of esoteric knowledge. Access, however, was closely guarded. Outsiders have known little until the last few decades when a flood of previously hidden texts have begun to appear. Nevertheless, enemies knew enough that a common pejorative name for the Ismailis was B??in?s “Esoterists” (i.e. the B??iniyya), a term based frequently on scurrilous distortions of the truth. This situation begun to change. Panels at Shi’i studies conferences have considered aspects of the subject. One important book explores carefully the social significance of the Ismaili use of ta’w?l in an early context. Papers by Poonawala and others have helped elucidate important aspects. But, in one sense these efforts, as valuable as they have proven to be, have only opened a window onto how vast and varied this doctrine was. We can begin to see a rich array of types, of ways to perform ta’w?l, by whom, and under what control. But once permitted access what kind of knowledge results? Is it truly esoteric, i.e. unconnected to the outward ??hir? text by some form of logic (e.g. a metaphoric extension of meaning)? Or is the newly revealed truth gained by a rite of initiation that leads to something that transcends what might be ordinarily understood, or even to a different and new form of knowledge altogether? What is needed now is a guide into this material with set of waymarkers showing what leads where, and when are we dealing with a religious phenomenon non-initiates might comprehend, or conversely, is it an impenetrable mystery from which we are excluded. Or is it both depending on circumstances, opportunities and conditions. We know already enough to claim there is no single or simple answer. The process was ongoing and it varied considerably; the application of ta’w?l served a range of functions: instrument of social cohesion, test of loyalty proven by willingness to contribute funds, an understanding of religious matters at a superior level, membership in an intellectual elite. The present paper provides just such a guide through a comprehensive survey of the many dimensions of this subject.