PubMed, available via the NCBI Entrez retrieval system, was developed by the National Center for Biotechnology Information (NCBI) at the National Library of Medicine (NLM), located at the National Institutes of Health (NIH). Entrez is the text based search and retrieval system used at NCBI for all major databases including PubMed, Nucleotide, and Protein Sequences, Protein Structures, Complete Genomes, Taxonomy, OMIM and many others. PubMed was designed to provide access to citations from biomedical literature. Subsequently, a linking feature LinkOut, was added to provide access to full-text articles at journal web sites, and other related web resources. PubMed also provides access and links to the other Entrez molecular biology databases. Publishers participating in PubMed electronically submit their citations to NCBI prior to or at the time of publication. If the publisher has a web site that offers full-text of its journals, PubMed provides links to that site, as well as, biological databases, consumer health information, research tools, and more. There may be a charge to access the text or information. In addition, PubMed provides a Batch Citation Matcher, which allows users to match their citations to PubMed citations, using bibliographic information such as journal, volume, issue, page number, and year. Database Coverage PubMed provides access to bibliographic information which includes MEDLINE as well as: The out-of-scope citations (e.g., articles on plate tectonics or astrophysics) from certain MEDLINE journals, primarily general science and chemistry journals, for which the life sciences articles are indexed for MEDLINE. Citations that precede the date that a journal was selected for MEDLINE indexing. Some additional life science journals that submit full text to PubMedCentral and receive a qualitative review by NLM.