The Dewey Decimal System is a way to organize books in libraries. Created by Melvil Dewey in 1876, it uses a three-digit number to classify subjects. For example, books about history might be assigned numbers starting with 900, while books about science start with 500. This system helps people find books easily and keeps similar topics together. Each number in the Dewey Decimal System can be further divided into more specific categories. For instance, within the 500s, you might find 510 for mathematics and 520 for astronomy. This detailed organization makes it simple for readers to locate the information they need in a library.