The collections of the National Library of China can be divided into three general classes, i.e. preservation copies, basic collection copies and lending copies. The preservation copies are collected for long-term preservation and are not allowed for circulation. The basic collection copies can be circulated for reading, but not for lending. Both the preservation copies and the basic collection copies comprise the permanent assets of documents of the library. The lending copies are acquired for lending purposes, and can be discarded according to their usages. We can say that all the first copies of Chinese publications are considered to be preservation copies, the second copies are considered to be basic collection copies, and the remaining copies are considered to be lending copies.