An ISBN, or International Standard Book Number, is a unique identifier for books. It helps publishers, booksellers, and libraries easily find and manage books. Each ISBN is made up of 13 digits, which can tell you information about the book, such as the publisher and the edition. When you see an ISBN on a book, it ensures that you are looking at a specific title and version. This system is essential for organizing the vast number of books available today, making it easier for readers to locate their desired titles in stores or online.