Dewey Decimal System Explained: A Simple Way to Make the Library's Catalog Work for You

I worked in a library for about 5 years. In that time, I helped a lot of patrons who seemed baffled by the intricacies of the Dewey Decimal system-the most common way to organize nonfiction in public libraries. Trying to understand the whole thing at once can be daunting. But the key is, you don't need to understand it all, just the parts that are right for you.

Here's a brief overview of how the system works and how it can work for you.

How it works:

1. Every book has a number, called the "call number," that tells you where it is.

2. That number is between 000 and 900 and may have several decimal places.

3. The hundreds represent broad topics, the tens represent subtopics, the ones represent really subtopics, and the decimal places represent sub sub sub topics.

4. For example, a book on American cooking (as long as it's marketed as "American" and not "vegetarian" or "BBQ" for example) would have the call number 641.5973. The 600s are sometimes called technology or applied science, but I think that doesn't really capture what they're about-there's books on medicine, space travel, gardening, pets, cooking, business, and more in the 600s.

640s are generally called "Home Ec." or "family living." So they've got things like frugal living, cooking, sewing (for practical uses, not for art), child-raising, and the like. 641 is specifically cooking. And .5973 is where they put books on American cooking. "973" is a designation for America, so the .5973 actually makes some sense.

Wow that was complicated, right? It's ok, you don't have to know all those little details, because you can make the system work for you.

Making it work for you:

Next time you get a book from a section you frequently use, look at its Dewey number. I check out a lot of books on personal finance. The number for that is 332.024. Now I know that most PF books will be in that section. If I go to another library, I know right where to look. Use the library's database, card catalog, or reference librarian to get you started.

Don't feel overwhelmed. This will just be for the sections you like. If you're into travel, you may become very familiar with 910-919, but know nothing about the computer section 004-006.

Being familiar with the sections you like gives you flexibility. You don't have to be looking for a particular book, but you know exactly where to go. Sometimes I wander into religion or personal finance and just browse.

When I moved, this summer, I was able to start using my new library right away. I saw where they kept nonfiction and immediately found the types of books I was looking for.

Using the library isn't about memorizing categories and subcategories. It's about knowing what you like and remembering where it is. It's about being open to absorbing new information which you can use later.

If you'd like to have a list of the overall categories for reference, I'm including Wikipedia's version below with a few of my comments.

000 - Computer science, information, and general works
100 - Philosophy and psychology
200 - Religion (if you're looking for religion other than Christianity, they're all in the 200-210s or 290s. Christianity, in its many forms, takes up from 220-289.)
300 - Social sciences (politics, crime, finance, immigration, SAT study guides)
400 - Language
500 - Science (these are the "pure" sciences, like chemistry or biology)
600 - Technology ("applied sciences" like I talked about above)
700 - Arts and recreation (includes sports and cartoon collections)
800 - Literature (some classic literature, poems, plays, short stories, how to write a novel and such, foreign literature)
900 - History and geography (910-919 is mostly travel guides, in my experience. American history is 973 (970 if you include first nations) through 979)