A call number is a unique identifier assigned to each book in a library, which acts like an address and tells us where the book is located in the library. Call numbers appear on the spines of books and journals and in the librarys catalog. They are made up of letters and numbers that follow a pattern, and each part of the call number signifies specific information about the book. The most commonly used call number system is the Library of Congress (LC) classification system. The first sections of the call number represent the subject of the book, while the letter-and-decimal section of the call number typically represents the authors last name. The last section of a call number is often the date of publication. Call numbers are arranged in a specific order on library shelves, so books on similar subjects are shelved near each other. To find a book using its call number, you need to read the call number from left to right and follow the sequence until you have located the book. Once you have a call number for your book, you can use the librarys floor plan or maps to find the area of the library where you can find the book.