The Library of Congress Classification (LCC) LC Call Number System is a classification system that is used by most academic libraries in the United States. It is currently one of the most widely used library classification systems in the world. The LCC system divides all knowledge into twenty-one basic classes, each identified by a single letter of the alphabet. Most of these alphabetical classes are further divided into more specific subclasses, identified by two-letter, or occasionally three-letter, combinations. The NVCC library uses the Library of Congress Classification Call Number System.