The United States National Library of Medicine (NLM), operated by the United States federal government, is the world's largest medical library. Located in Bethesda, Maryland, the NLM is an institute within the National Institutes of Health.

Its collections include more than seven million books, journals, technical reports, manuscripts, microfilms, photographs, and images on medicine and related sciences, including some of the world's oldest and rarest works.

The National Library of Medicine runs the National Center for Biotechnology Information, which houses biological databases that are freely accessible on the Internet through the Entrez search engine.

According to en.wikipedia