NLM: The U.S. National Library of Medicine is operated and managed by the U.S. federal government and is the largest medical library in the world. It was formerly known as the Library of the Office of the Secretary of Public Health, which was established in 1836. It is located in the National Institutes of Health in Bethesda, Maryland. This library was established in 1836 and has a collection of nearly 12 million titles.