The (rNying ma'i rgyud 'bum) contains many of the oldest examples of Tantric literature in Tibetan. It also contains many of the most important examples of Buddhist Tantric literature surviving in any language. Its contribution to Tibetan religion and culture over the last 1,200 years has been incalculable, and remains undiminished today. Yet, like most manuscript traditions of such great antiquity, centuries of accumulated scribal corruption have reduced them in a great many cases to near incomprehensibility, even for the most learned Tibetan lamas. The modern period has been a particularly challenging time for this great scriptural tradition, above all because the Chinese entry into Tibet led to the destruction of an estimated ninety-five percent of its extant witnesses. In this work, Cantwell and Mayer have begun the immense task of restoring these wonderful texts to their original form through textual criticism. The present scribal state of the texts, the surviving editions, and the various possible methods of restoring them through textual criticism are discussed. Editions of two important texts have been produced, which also consider features of the original compilation and their commentaries. This is intended to be a small contribution towards the eventual restoration of the entire tradition.