Taoist immortals can be divided into four classes according to their level of cultivation. At the lowest level are the human immortals. Human immortals are not very different from ordinary mortals except that they live long and healthy lives. In this book, Fan Li, Hsi Shih, and Kiang Tzu-ya are examples of human immortals.
Next come the earth immortals. These immortals live for an unusually long period of time in the mortal realm, far beyond the life span of ordinary people. In this book, Tso Chi, Fei Chang-fang, and Chang Chung are examples of earth immortals.
Above the earth immortals are the spirit immortals, who live forever in the celestial lands. Some, like the Yellow Emperor, Wei Po-yang, and Wen Shih, take their bodies with them when they enter the immortal realm. Others, like Pal Yu-ch'an, Kuo P'u, and Chang Po-tuan, leave their bodies behind when they liberate their spirits.
At the highest level are the celestial immortals. These immortals have been deified and given the titles of celestial lord, emperor, or empress. Some, like Lao Tzu and Chuang Tzu, are de facto deities because they are considered manifestations of the cosmic energy of the Tao. Others, like Lu Tung-pin and Ho Hsien-ku, were "promoted" to deity status because of the meritorious works they had done in the mortal and immortal realms.