One of the confusing things about libraries is our use of the Dewey Decimal System. It doesn’t help matters that some books, namely fiction and biographies, are actually arranged alphabetically. That means that when you are looking for nonfiction, you must use the online catalog to find where a book is shelved. However, when you are looking for fiction or biographies, you can find books shelved under the last name of the author (for fiction and graphic novels) and by the last name of the subject (for biographies, autobiographies, memoirs and letters). And since the New York Public Library has nearly 90 branches, some with multiple floors and multiple collections, you also need to take note of which branches and collections have your book before you know where to go. Never fear! Read this blog entry, watch this video or talk to a librarian if you need help.

What exactly is a Dewey decimal number? It is a numerical code that consists of three digits, followed by a decimal, then usually zero to four digits following the decimal. For example, 759.13 is the Dewey decimal number for American painters.

Do these numbers mean anything? Yes! The first three digits indicate the category under which the book is classified. For example, the 500s are for natural sciences, the 700s are for the arts and the 800s are for literature. Numbers within these ranges refer to more specific subjects. (759 is the number for painters). And then the numbers after the decimal make it even more specific (13 is the code for the United States). After the number, you will find a letter or a word. Sometimes there can be hundreds of books with the same Dewey decimal number, so we add a letter, usually the first letter of the author’s last name, to help you find your book more quickly.

Why group things by number? Can’t you just arrange books by title or author? Of course we can, but that would mean that you would need to tell us the title or author of the book you are looking for before we can tell you where to find it. With the Dewey decimal system, you can look for books by subject: say you are looking for books on diabetes. If you go to Barnes and Noble and ask for books on diabetes, they’ll just tell you to go to the Health section. With the Dewey Decimal System, we can tell you exactly where to go.

Of course there are caveats: the system was invented over 100 years ago, and although it is continually being modified, it can never meet the rapid pace of knowledge and civilization. Because of the specific nature of the system, sometimes you will need to go to more than one section to find everything that you can on a subject. Finally, looking for numerical labels on the shelf is not easy on the eyes.

Overall, though, the system works great. The system is flexible and generally easy to understand. People are always finding books that they never knew existed. And that’s the magic of the Dewey Decimal System.