(provided by Derek from lisiming.com)
In the quest for longevity and immortality, Chinese, like other ancient civilizations such as Egypt, Arab, Greece, and the Middle Age Europe, had embarked on the journey of Alchemy, which in dictionary is defined as the methods for transmuting baser metals into gold and with finding a universal solvent and an elixir of life.
In Daoist tradition, there are two types of Alchemy, namely External Alchemy (外丹) and Internal Alchemy (内丹). External Alchemy refers to the cooking and fusion of external metal and chemicals to produce medicine for immortality, and Internal Alchemy refers to the cultivation and transformation of internal essence-energy-spirit (three treasures) to achieve longevity and immortality.
The external alchemy, like the many attempts in other countries throughout history, had not been successful in terms of achieving longevity and immortality, and in many cases had led to the killing of people due to metal/chemical poisoning. Internal alchemy, on the other hand, had aid countless people achieve health and longevity, as reported by Daoist Internal Alchemy masters such as Wei BoYan 魏伯阳(~151A.D.-?), LuDongBin 吕洞宾 (796A.D-?), ZhangBoDuan 张伯端 (983-1082A.D.), LiDaoChun 李道纯(1277-1305A.D.) and ZhangSanFeng 张三丰(1247-1458A.D.).
Internal Alchemy: 5 stages
Over the years Daoist had classified Internal Alchemy into 5 Stages: Building Foundation (筑基), Transform Essence into Energy (炼精化气), Transform Energy into Spirit (炼气化神), Transform Spirit back to Nothingness (炼神还虚), and Transcend Nothingness in accordance to Dao (炼虚合道). Building Foundation refers to the acquiring and understanding of the essential knowledge about one self and reality, and to the basic healing of the body and the mind. Transform Essence, Energy, and Spirit refer to the owning, mastering, and transcending of body, mind, and consciousness respectively. Transcend nothingness refers to transcending of all attachment/aversion/identification and live in accordance to Dao.
Internal Alchemy: 4 Approaches
To cater for the diversity of background and stage of spiritual development, countless Internal Alchemy methods had been invented over the history to suit people with different needs. LiDaoChun (李道纯), master of QuanZhen Middle Branch (全真中派) in the 13th Century, had classified various Daoist practices into 9 side tracks and 4 main approaches. The 4 main approaches consist of the Lower, Middle, Upper and Highest Approach.
Lower approach (下乘) focuses on the alchemy of physical body, which when couple with sentiment transcendence could nurture life. The middle approach (中乘) focuses on the alchemy of energy body, which when practice ceaselessly could extend life. The upper approach (上乘) focuses on alchemy of body and mind, which represents a high road to longevity, and when practice single-heartedly could lead to immortality. The highest approach (最上一乘) focuses on the alchemy of mind, consciousness and nothingness, which is the pathway for Outmost person, and leads to Dao realization. (Source: Li Daochun, Zhongheji/Book of Balance and Harmony, Chapter 2. 李道纯, 中和集, 卷二)