Born on this day in Adams Center, New York, librarian Melville Louis Kossuth Dewey (1851–1931) later shortened his name to Melvil. At just twenty-one years old, he invented the famous decimal system of library book classification that still bears his name, turning shelves of scattered titles into a navigable world of ideas.

The Dewey Decimal Classification (DDC) system groups books by topic, divides them into ten main classes (000–999), then breaks each class into more specific subjects. Every library book is given a unique call number, an address that helps readers find exactly where a book lives on the shelf.

Dewey’s original ten classes included:

000 Generalities
100 Philosophy and Psychology
200 Religion
300 Social Science
400 Language
500 Natural Science and Mathematics
600 Technology (Applied Sciences)
700 Arts
800 Literature
900 Geography and History

In 1876, Dewey helped shape the future of librarianship by supporting a national library association to improve library and information services and by publishing one of the first professional library journals. Eleven years later, he established a pioneering professional library school at Columbia University, training generations of librarians to guide readers through the stacks.

“A great librarian must have a clear head, a strong hand, and above all, a great heart… and I am inclined to think that most of the men who achieve this greatness will be women,” he once said. Behind his love of order was a deep respect for the people who brought books and readers together.

For Dewey, a library was never just a building. It was a living map of human thought, a place where classification became invitation, and where each shelf could quietly remind us that knowledge, curiosity, and community are among the true necessities of life.