The numbers of nonfiction books are based on the Dewey Decimal System created by Melvil Dewey. He decided books should be grouped together according to their subject. There are ten different groups:

000-099
Books with many subjects all in one book, such as World Book Encylopedia, Book of Knowledge; also books on the newspaper and reporting.

100-199
Books on feelings, and how to study, thoughts and ideas.

200-299
Religion

300-399
Government, laws, folklore, holidays, fairy tales

400-499
English grammar, foreign languages

500-599
Mathematics, astronomy, earth, planets, birds, plants, wild animals

(science that occurs naturally)