The Buddha himself said in a Lesser Vehicle sutra: "Son of the family! You are to become expert in the skandhas. You are to become expert in the ayatanas. You are to become expert in the dhatus. You are to become expert in pratityasamutpada. You are to become expert in topics. You are to become expert in non-topics." With these words, the Buddha indicated that there are six topics which must be learned, at least to some extent, by every one of his followers. Although the Buddha gave these teachings in the Lesser Vehicle, they are a necessary foundation for practitioners of all levels, from those studying the Lesser Vehicle to those practising Mahamudra and Great Completion. This book gives a thorough explanation of the six topics using a text written by Zhanphen Chokyi Nangwa, or Khenchen Zhan-ga as he is more commonly known, the greatest of all abbots to have presided over the famous Shri Singha monastic college at Dzogchen Monastery, Tibet. The author of the book, the well-known teacher and translator Tony Duff, supplements the explanations in the text with many clarifications in an extensive introduction. The text is very similar to Mipham Namgyal's famous "mkhas 'jug" or Gateway to Knowledge as it has been called. Unfortunately, Mipham's text is difficult for beginners. Zhan-ga's text is quite different; it was not written merely as a piece of scholarship, but was carefully composed so as not to exclude beginners with excessively difficult explanations and moreover to be helpful to practitioners of all levels. For these reasons, Gangteng Tulku has selected our book rather than Mipham's Gateway of Knowledge in order to teach this topic to students in the second year of his shedra. Extensive explanations of the meaning of the six topics are provided by the author from his own knowledge gathered during forty years of studying with the Gelug, Kagyu, and Nyingma traditions, not to mention his extensive stays at Dzogchen Monastery where he learned the approach of Zhan-ga directly from Zhan-ga's successors. Ample footnotes, an extensive glossary, and a carefully corrected edition of the Tibetan text are also provided.