Taoist alchemy comprises two main branches: Waidan (External Alchemy), which involves the manipulation of minerals and metals, and Neidan (Internal Alchemy), where the entire process occurs within the practitioner. In Neidan, the practice centers on the symbolic inversion of natural time cycles to restore them to their origin. Supported by numerical and graphic emblems, this inversion is conceived as entirely “rational” within the framework of classical Taoist views on the origin and unfolding of those cycles.

Looking at this and other aspects of Neidan allows one to discern some of its essential features. At the same time, examining Neidan in relation to present-day studies of Esotericism—also in light of current efforts to extend this field beyond its Western scope—poses significant challenges. First, one should assess whether and to what extent Taoist alchemy is genuinely “esoteric.” Second, Neidan cannot be accurately interpreted through Western paradigms or subsumed into the construct of an imagined “Eastern Esotericism.” Finally, the language barrier compels scholars unfamiliar with Chinese to depend on translations and studies of varying reliability. A prime example of all three issues mentioned above is the Secret of the Golden Flower, the best-known Neidan text in the West through Richard Wilhelm’s translation and C.G. Jung’s commentary.