The twenty-one Semdzins of the Upadesha series of Dzogchen teachings are one of the main practices for obtaining a precise understanding of the state of contemplation in non-dual presence or rigpa. The great master Longchenpa gave a detailed explanation of the twenty-one Semdzins in the Theg mchod mdzod. It was on the basis of this text that Chogyal Namkhai Norbu taught and gave a commentary on the Semdzins during a retreat held at Merigar West over Easter 1989. These teachings constitute the fundamental core of this book, which also comprises explanations taken from teachings given in July 1977 at Prata, Italy. The Semdzin Yugu contained in the first appendix, which belongs to the Upadesha teachings traditionally ascribed to the great master Shri Simha, has been taken from a teaching given at Merigar West in August l985.