Many libraries use the Dewey Decimal System to organize non-fiction books on their shelves. This number system was invented by Melvil Dewey in 1876. Each number, from 000 to 999, stands for a subject. These numbers keep all the books on a subject together on the library shelves. The call number is on the back of the book so that it can be seen on the shelf.
Many books have the same call number because their subjects are the same.
The author's name is then added. The books are shelved alphabetically by the authors' names.