The Dewey Decimal Classification (DDC) is a system used to organize library materials by assigning a unique number to each subject. Developed by Melvil Dewey in 1876, it divides knowledge into ten main classes, each represented by a three-digit number. These classes cover broad topics, such as literature, science, and history, making it easier for users to find books on specific subjects. Each main class is further divided into subclasses and specific topics, allowing for detailed categorization. For example, the class for social sciences is numbered 300, while psychology falls under 150. This hierarchical structure helps libraries maintain order and facilitates efficient information retrieval.