In the publishing world, buying and selling book numbers usually referred to the owners of book numbers selling their book numbers to other companies or individuals in order to obtain higher profits. These book numbers might have already been used by other companies or individuals or could no longer be used for some reason. However, buying and selling book numbers was illegal. According to the provisions of the "People's Republic of China's copyright law", the owner of the book number has the right to publish, distribute, and transmit his work. Unauthorized use of another person's book number is an act of copyright violation. Therefore, if they bought or sold the book number, they would be fined by the copyright department or have other legal consequences. Although buying and selling book numbers could bring high profits in some cases, it was not a legal act from a legal point of view. It is recommended not to engage in any activities related to the sale of book numbers to avoid legal risks.