"This book presents for the first time a translation of the complete Expository Commentary to the Daode jing written by the Daoist Cheng Xuanying in the 7th century CE. This important commentary is representative for Tang Dynasty Daoist philosophy and Daoist Twofold Mystery philosophy, also called chongxuanxue. Following the philosophical tradition of xuanxue authors like Wang Bi, Cheng Xuanying read the Daode jing using a framework of the then current Daoist religion. His conceptual framework included the assumption that Laozi had written the Daode jing to guide the beings to unite with the Dao and thereby reach ultimate salvation. Salvation is interpreted as a metaphysical form of immortality, reached by overcoming the dichotomy of being and non-being, and thus also life and death. He thus connects epistemological concerns with soteriological concerns. The process proposed to overcome these dichotomies relies on reasoning along the lines of tetralemma logic, a form of reasoning that had become known in China mainly through the Buddhist Madhyamika çâsastras. One of Cheng Xuanying's prominent commentarial strategies is therefore the consistent application of tetralemma logic in his reading of the Daode jing. His philosophical outlook ties together the ancient text of the Daode jing and the more recent developments in Daoist thought, which to a rather large extent occurred under the influence of an intense interaction with Buddhist ideas"--