PubMed is a free online directory that provides access to MEDLINE, the National Library of Medicine's database of citations and abstracts for various medical studies. Over 25 million citations and abstracts are accessible through PubMed as of 2015.
The National Library of Medicine has been documenting medical research since 1879. This information was eventually collected in a database known as MEDLINE, which provides journal citations and abstracts for literature from various medical fields including nursing, dentistry, veterinary care and preclinical sciences. PubMed has provided the public with access to MEDLINE since 1996, along with access to a small selection of citations for sources not available through MEDLINE.