In his masterful introduction to the body of this work, Tulku Thondup covers the three outer and inner tantras, the three divisions of Atiyoga, Dzogchen, and the other yanas and traditions. He includes excerpts from the exemplary lives of teachers (such as Longchen Rabjam) to illustrate the ways of training in Dzogchen.
Thorough, overwhelming, but unreadable in a few sittings. I hated the interrupted, extended quotation-prose style of writing. This is great as a sourcebook for esoteric and difficult to translate sutras and tantric terma-texts.