NPR’s On the Media examines the Dewey Decimal Classification System, a method that dates back to 1876 and is used by most libraries around the world. The second most popular system, the Library of Congress Classification System, was published in the early 1900s and based on the organization of Thomas Jefferson’s personal library. These systems help patrons find books on the shelves and facilitate resource-sharing between libraries. But they also encode bias into the structure of libraries.