This book contains four essays on Internal Alchemy by Isabelle Robinet, originally published in French and translated here for the first time into English. The essays are concerned with the alchemical principle of "inversion"; the rhetorical and linguistic devices by Chinese alchemists to "give form to the Formless by the word, and thus manifest the authentic and absolute Dao"; the symbolic function of numbers in Taoism and in Internal Alchemy; and the original meanings of the terms External Elixir (waidan) and Internal Elixir (neidan).