This study presents the first complete translation of Liu Chuxuan's (1147-1203) commentary on the Yellow Emperor's Scripture of Hidden Contracts (Huangdi Yinfujing Zhu). Liu Chuxuan numbers among the famous seven disciples of Wang Chongyang, who is Quanzhen Daoism's founder and one of the most revered figures in religious Daoism. Today one of the two surviving Daoist sects, Quanzhen Daoism was a revolutionary religious movement when it began in the days of the Jin-dynasty. Liu Chuxuan's commentary constitutes an important document for the history of Quanzhen Daoism. First of all, it is one of the few surviving commentaries on a classical Daoist scripture written by a proponent of early Quanzhen. Secondly, Liu Chuxuan's commentary provides insight into the central ideas of internal alchemy, a theory of self-cultivation promoted by early Quanzhen Daoism. On top of that, the commentary's eclectic nature elucidates an important trait of Quanzhen Daoism. It integrates sources from the three different religious traditions of China: Daoism, Confucianism and Buddhism. This eclecticism reflects on a general tendency of Chinese culture in the days of the Jin-dynasty. The "unification of the three teachings" was prevalent in the entire society and, until this day, comprises an important aspect of Chinese thought.