Wikipedia
Daozang (; Wade-Giles: Tao Tsang), meaning " Taoist Canon", consists of around 1,400 texts that were collected c. 400 (after the Dao De Jing and Zhuang Zi which are the core Taoist texts). They were collected by Taoist monks of the period in an attempt to bring together all of the teachings of Taoism, including all the commentaries and expositions of the various masters from the original teachings found in the Tao Te Ching and Zhuangzi. It was split into Three Grottoes, which mirrors the Buddhist Tripitaka (three baskets) division. These three divisions were based on the main focus of Taoism in Southern China during the time it was made, namely; meditation, ritual, and exorcism.
These Three Grottoes were used as levels for the initiation of Taoist masters, from lowest (exorcism) to highest (meditation).
As well as the Three Grottoes there were Four Supplements that were added to the Canon c. 500. These were mainly taken from older core Taoist texts (e.g. Tao Te Jing) apart from one which was taken from an already established and separate philosophy known as Tianshi Dao (Way of the Heavenly Masters).
Although the above can give the appearance that the Canon is highly organized, this is far from the truth. Although the present-day Canon does preserve the core divisions, there are substantial forks in the arrangement due to the later addition of commentaries, revelations and texts elaborating upon the core divisions.