Periodical number, also known as periodical code or ISSN (international standard serial number), refers to the digital code used to uniformly identify continuous publications. Each periodical has a unique periodical number, which consists of eight digits and is divided into two four-digit groups separated by a "-"sign. Periodical number is the basic element of periodical publication, distribution and indexing, which can help readers find the required periodicals and articles accurately.

Periodical number is an important standard in the field of periodicals, which is usually issued by the issuing agency authorized by the International Organization for Standards. At present, more than 227 countries and regions in the world have periodical number distribution institutions, among which national libraries or national publishing bureaus are the main ones. Through the periodical number, we can know the publishing house, publication year, number of issues and other information of a periodical, and also facilitate the management, evaluation and citation of the periodical.

In the era of digital reading, the importance of periodical number is more prominent. Many digital libraries, electronic periodical databases and retrieval tools expect to retrieve and distinguish periodicals by their serial numbers. Periodical publishers and scientific research institutions also pay more and more attention to the use of periodical numbers. Through the use of periodical numbers, users can find the periodical resources they need conveniently and quickly, while ensuring the accuracy of periodical copyright and information.