PubMed Central is a free digital database of full-text scientific literature in biomedical and life sciences. It grew from the online Entrez PubMed biomedical literature search system. PubMed Central was developed by the U.S. National Library of Medicine (NLM) as an online archive of biomedical journal articles.

The full text of all PubMed Central articles is available free. Some participating publishers, however, delay release of their articles for a set time after paper publication (often six months).

As of July 2011^[update], the archive contains approximately 2.2 million items, including articles, editorials and letters. It appears to be growing by at least 7% per year.^{[citation needed]} As of September 2004^[update], PubMed Central, PubMed, and related NLM services were handling approximately 1,300 hits per second, and supplying 1.3 terabytes of data per day.

The repository has grown rapidly, as the U.S. National Institutes of Health's "Policy on Enhancing Public Access to Archived Publications Resulting from NIH-Funded Research" is designed to make all research funded by the National Institutes of Health (NIH) freely accessible to anyone, and, in addition, many publishers are working cooperatively with the NIH to provide free access to their works. In late 2007, the Consolidated Appropriations Act of 2008 (H.R. 2764) was signed into law and included a provision requiring the NIH to modify its policies and require inclusion into PubMed Central complete electronic copies of their peer-reviewed research and findings from NIH-funded research. These articles are required to be included within 12 months of publication. This is the first time the US government has required an agency to provide open access to research and is an evolution from the 2005 policy, in which the NIH asked researchers to voluntarily add their research to PubMed Central.