Except the authenticDao Zang(Taoist Canon), all other Taoist books that are not included inDao Zangare called asZang Wai Dao Jing(Canons Left Out ofDao Zang).
Numerous books are not includedDao Zang. There are many reasons thatDao Zangdid no include these books. Some canons had been available at that time and should be compiled intoDao Zang, but they were left out because of various subjective reasons. Some other canons came into being after the compilation ofDao Zang.
The canons left out ofDao Zangare very useful materials for research on China's traditional culture and Taoism. Many of them are important and excellent writings. For example,Shen Xian Zhuan(Biographies of the Immortals) by famous Taoist Ge Hong was included in various Chinese ancient books, but it was not included inDao Zang. The book is of great importance for research on the religious philosophy and social thoughts of that time. Another example is that only a few writings of Chen Tuan, a famous Taoist of the 10thcentury who was calledLao Zu(ancestor) of the Taoism by later generations, were included inDao Zang.Taiping Jing(Classic of Great Peace) is a very important classic of Taoism, but only fewer than 1/3 of its contents are collected intoDao Zang.
In the past several decades, more and more personages in the Taoist field strived to add new contents intoDao Zangor recompile it. All of them find that it is a very urgent and significant task.