What Is a DOI? How to Find One and Use It to Get a Paper

A DOI, or Digital Object Identifier, is a permanent ID for a piece of research. Almost every journal article published in the last two decades has one. It looks like this: 10.1038/nature12373. If you have a paper's DOI, you can find that exact paper anywhere, which makes it the most reliable thing to search with.

What the parts mean

A DOI has two halves, separated by a slash.

• The prefix always starts with "10." followed by a number, such as 10.1038. It identifies the organisation that registered the DOI, usually the publisher.
• The suffix is everything after the slash. The publisher chooses it, so it can be short and tidy or long and full of punctuation.

DOIs are not case sensitive, so 10.1038/NATURE12373 and 10.1038/nature12373 are the same paper.

Why DOIs exist

Web addresses change. Journals move between publishers, sites are redesigned and old links break. A DOI stays the same for good, and the publisher keeps the record behind it pointing at the paper's current location. Put https://doi.org/ in front of any DOI and you have a link that should always lead to the paper.

DOIs are issued through registration agencies. Crossref handles most journal articles, books and conference papers, and DataCite handles most datasets and many preprints.

Where to find a paper's DOI

• On the article's web page. It is usually near the title, the author list or the citation details, often shown as a doi.org link.
• On the PDF. Look at the header or footer of the first page.
• In a reference list. Modern citation styles put the DOI at the end of each reference.
• In the web address. Many publishers include the DOI in the URL of the article page. Anything from "10." onwards is the DOI.

If you cannot find one, search for the paper's title in our finder, which will look the DOI up for you.

Papers without a DOI

Older articles, some conference papers, theses and reports may have no DOI at all. In that case, search by title instead. Other fields have their own identifiers, which also work as a starting point:

• arXiv IDs, such as 1706.03762, identify preprints on arXiv. Every arXiv paper also has a DOI, formed by adding the ID to the prefix 10.48550/arXiv.
• PMIDs are the numbers PubMed gives to biomedical articles, and PMCIDs (starting with "PMC") identify full-text articles in PubMed Central.

You can paste an arXiv, PubMed or PubMed Central link into the finder directly.

Using a DOI to get a free copy

Following a doi.org link takes you to the publisher's page, which is where the paywall is. To find out whether a free copy exists elsewhere, paste the DOI into the finder on our home page. It checks the open-access indexes for copies in repositories and preprint servers, and links you straight to one if it exists. Our guide to reading research papers for free covers what to do when it does not.