MEDLINE is a database that houses millions of health care-related journal articles. It is operated by the United States National Library of Medicine and is an offshoot of the website PubMed.

MEDLINE contains resources dating back to 1946. Articles are pulled from thousands of journals published worldwide in around 60 languages. Around 2,000 to 4,000 new references are added to MEDLINE every day as of 2015. Each citation is updated to use the most current medical subject headings to neatly archive materials.

Searchable articles on MEDLINE focus on the broad categories of biomedicine and health. This not only covers life, behavioral and chemical sciences, it expands to topics such as health policy development, public health, research, clinical care and bioengineering. It also spans into areas of environmental science, marine biology, and plant and animal science.

Many articles referenced on MEDLINE are available for free from the PubMed archives; however, some are available only through ordering a specific journal. Articles requiring payment can be purchased through the Loansome Doc section of PubMed.

Both MEDLINE and PubMed started as a monthly guide called Index Medicus compiled by the National Library of Medicine in 1879. It evolved into MEDLARS Online, a searchable database located in libraries that included around 240 medical journals to be accessed by 25 users at a time. With the development of the Internet, PubMed became a free database available to any user. MEDLINE was later developed and marketed more to professionals than laypeople.