If you've been to the library you know we have a LOT of books, and if you've been to the reference desk you know that we can usually guide you directly to the area for a topic you're interested in or to a specific book. This is possible not because librarians know everything, but because we know how to use the Dewey Decimal System.
The first thing to know about Dewey is that it uses numbers to represent subjects. Almost any subject you can think of has a corresponding Dewey number. We use Dewey to organize nonfiction materials at all of the Oakland Public Libraries. Other sections (like fiction, biography, and test prep) are arranged alphabetically.
Each book in the nonfiction section has its own Dewey call number, which makes it easy to find the area for a topic or to find a specific item. You can browse all the cookbooks or all the sheet music, but you can also go straight to the book you want.
Dewey numbers are formed one digit at a time, starting from the left.