PubMed created by the U.S. National Library of Medicine (NLM), is the search interface for MEDLINE, NLM's journal citation database. PubMed citations come from 1) MEDLINE indexed journals, 2) journals/manuscripts deposited in PubMed Central (PMC), the free digital archive of biomedical and life sciences journal literature and 3) the National Center of Biotechnology Information (NCBI) Bookshelf (free online books). Both MEDLINE and other PubMed citations may have links to full-text articles or manuscripts in PMC, NCBI Bookshelf, and publishers Web sites.