NLM Classification

The NLM Classification is a library classification system developed by the National Library of Medicine for organizing materials in the fields of medicine and related health sciences. Used internationally by medical libraries, it works in coordination with the Library of Congress Classification to provide comprehensive coverage: NLM handles biomedical subjects while deferring to LC schedules for non-medical topics.

Background

The NLM Classification was first published in 1951 by what was then the Armed Forces Medical Library (later renamed the National Library of Medicine in 1956). It was created to address the need for a classification scheme specifically tailored to the biomedical literature, as the Library of Congress Classification's coverage of medical subjects was deemed insufficient for a specialized medical library of NLM's scope. The classification has been continuously revised since its first edition, with updates published in regular seasonal editions to reflect developments in medical science and practice.

Purpose and Scope

The NLM Classification is designed for:

• Shelf arrangement and call number assignment in medical and health sciences libraries
• Organization of biomedical literature in catalogues and bibliographic databases
• Subject access to medical, dental, nursing, pharmacy, and veterinary materials
• Classification of materials at the National Library of Medicine itself

The scheme covers preclinical sciences (anatomy, physiology, biochemistry, pharmacology, microbiology, pathology), all branches of clinical medicine (internal medicine, surgery, specialties), public health, nursing, and allied health disciplines. Materials on non-biomedical subjects held by libraries using NLMC are classified using the corresponding Library of Congress Classification schedules.

Structure and Notation

The classification uses an alphanumeric notation organized into two main schedule groups:

The QS-QZ range covers preclinical sciences, while the W-WZ range covers medicine and related subjects. Table G provides geographic subdivisions that can be appended to class numbers where local geographic arrangement is desired.

Current Edition

The classification is published in regular seasonal editions. The current version is the 2026 Winter Edition, which includes scope of revision notes, lists of added and canceled class numbers, and the full schedules searchable online.

Governance and Maintenance

The NLM Classification is maintained by the National Library of Medicine's Metadata Management Program. The editorial process involves regular revision of schedules to accommodate new medical disciplines, procedures, and areas of research. The 19th Century Schedule is preserved separately for historical classification of older materials. NLM provides a fundamentals tutorial and on-demand class for cataloguers learning the system.

Notable Implementations

The NLM Classification is used by the National Library of Medicine and by medical libraries worldwide. It is closely integrated with the Medical Subject Headings (MeSH) vocabulary, which serves as the subject heading counterpart for biomedical indexing. Libraries using the NLM Classification typically also assign MeSH terms for subject access, and the NLM Catalog provides lookup for records classified under the scheme.

Related Standards

• MeSH (Medical Subject Headings) -- the NLM's controlled vocabulary thesaurus, used alongside the classification for comprehensive subject description of biomedical literature.
• Library of Congress Classification -- used for non-biomedical materials in libraries that adopt NLMC for their medical collections.

Further Reading

• NLM Classification Home
• Outline of the NLM Classification
• NLM Classification Fundamentals Tutorial
• NLM Policy on Classification (PDF)